Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.arcetri.astro.it/~lt/preprints/haebe_atlas/haebe_atlas.ps.gz Äàòà èçìåíåíèÿ: Tue Sep 11 16:56:47 2007 Äàòà èíäåêñèðîâàíèÿ: Sat Dec 22 08:46:03 2007 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: helix nebula

A&A manuscript no.
(will be inserted by hand later)
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08(08.06.2; 08.16.5; 13.09.6)
ASTRONOMY
AND
ASTROPHYSICS
7.6.1998
A search for clustering around Herbig Ae/Be stars
II. Atlas of the observed sources ?
Leonardo Testi 1; ?? , Francesco Palla 2 and Antonella Natta 2
1 Division of Physics, Mathematics and Astronomy, California Institute of Technology, MS 105­24, Pasadena CA 91125, USA
2 Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I­50125 Firenze, Italy
Received xxxx; accepted xxxx
Abstract. We present large field infrared images of a
sample of 45 Herbig Ae/Be stars. Stellar parameters, such
as age and mass, have been derived for all of them in a
consistent way. The images have been used to identify stel­
lar groups or clusters associated with the Herbig Ae/Be
star. The results presented in this paper form the database
for a study of clustering around intermediate mass stars
(Testi et al. 1998).
Key words: stars: formation -- stars: pre­main sequence
-- infrared: stars
1. Introduction
We have conducted an extensive near infrared (NIR) sur­
vey of the fields around a large sample of Herbig AeBe
stars with the aim of detecting and characterizing the
properties of groups of young stars around intermediate
mass pre­main sequence stars. We were primarily moti­
vated by the expectation that at NIR wavelenghts, and
especially at K band, the reduced extinction would enable
the detection of embedded young stars born in the same
environment of (and possibly coeval with) the intermedi­
ate mass star. Existing NIR surveys are either focused at
the detection of close, d !
¸ 3500 AU, companions (Leinert
Send offprint requests to: Testi: Caltech, lt@astro.caltech.edu
? Based on observations collected at the TIRGO (Gorner­
grat, Switzerland) operated by the CAISMI--CNR, Firenze,
Italy, and at the NOT (La Palma, Canary Islands) operated by
the Nordic Optical Telescope Scientific Association (Denmark,
Finland, Norway, Sweden).
?? This research was partly conducted while L. Testi was at
the Dipartimento di Astronomia e Scienza dello Spazio, Univer­
sit`a degli Studi di Firenze, Largo E. Fermi 5, I­50125, Firenze,
Italy.
et al. 1997; Pirzkal et al. 1997) or are restricted to a lim­
ited sample of objects and cover smaller fields than our
survey (Li et al. 1994; Hillenbrand 1995).
In Testi et al. (1997; Paper I) we have presented the
first results obtained for a subsample of 19 objects. In the
present paper we present an atlas of all the fields observed
so far (45 total), which forms the database for our study
of the clustering around young, intermediate­mass stars
(Testi et al. 1998). In Sect. 2 and 3 we describe the sample
selection, the observations and data reduction. The results
of the observations are presented in Sect. 4, whereas notes
on individual sources are given in Sect. 5. We summarize
our results in Sect. 6.
2. Sample selection
The target stars have been selected from the catalogue of
Herbig AeBe stars of Th'e et al. (1994) to cover the widest
possible range of spectral types and to be easily observ­
able from the northern hemisphere. As shown in Fig. 1,
the observed sample covers rather uniformly the range of
spectral types between A7 and O9, with only two stars
(Z CMa, spectral type F5, and V645 Cyg, O7) outside of
this interval.
The 26 new target stars are listed in Table 1 (data on
the other 19 sources can be found in Tables 1 and 2 of
Paper I. For each star we report in Column 1 the name,
in Column 2 and 3 the coordinates at the 1950 equinox,
in Column 4 the spectral type, in Column 5 the distance
from the Sun, in Column 6 the projected physical size of
the observed field at the assumed distance, in Columns 7,8
and 9 the limiting magnitudes in the J, H and K bands, in
Column 10 the photometric accuracy and in Column 11
the completeness absolute magnitude M c
K (see discussion
below).
In Fig. 2 the galactic positions of the observed sources
(including the 19 listed in Paper I) are presented. There
appears to be no stronger selection effect, with the excep­

2 L. Testi et al.: A search for clustering around Herbig Ae/Be stars. II
Table 1. Observed Herbig AeBe stars.
TIRGO Observations
Star R.A. Dec. Sp. Dist Field Limiting Magnitude Acc. M c
K
(1950) (1950) type (pc) radius (pc) J H K (mag) a
Elias 1 04:15:34.5 +28:12:02 A6 160 0:16 17:6 16:5 16:4 8% 9:4
V1012 Ori 05:09:05.5 \Gamma02:26:24 B9 460 0:47 17:8 16:7 16:3 8% 7:0
HD 245185 05:32:24.1 +09:59:57 A1 400 0:41 17:5 16:2 16:8 7% 7:8
MWC 758 05:27:22.4 +25:17:43 A3 150 0:15 17:6 17:2 16:5 8% 9:6
V380 Ori 05:33:59.5 \Gamma06:44:46 B9 450 0:46 17:0 16:6 16:5 6% 7:2
RR Tau 05:36:23.8 +26:20:49 A3 800 0:81 17:5 16:5 16:3 5% 5:8
LkHff 208 06:04:53.2 +18:39:55 A3 1000 1:02 17:7 17:1 16:7 5% 5:7
VY Mon 06:28:21.0 +10:28:15 B8 800 0:81 17:7 16:9 16:4 6% 5:9
Z CMa 07:01:22.5 \Gamma11:28:36 F5 1150 0:67 16:6 15:7 15:7 20% 4:4
BHJ 71 23:03:07.0 +61:59:36 B0 730 0:74 18:1 17:1 16:6 5% 6:3
MWC 1080 23:15:14.6 +60:34:21 B0 2500 1:02 17:8 16:6 16:2 5% 3:1
NOT Observations
Star R.A. Dec. Sp. Dist Field Limiting Magnitude Acc. M c
K
(1950) (1950) type (pc) radius (pc) K (mag) a
MaC H12 00:04:25.2 +65:21:56.9 A5 850 1:05 17.0 3% 6:4
VX Cas 00:28:40.4 +61:42:17 A0 760 0:43 17.0 3% 6:6
RNO 1B 00:33:52.8 +63:12:29 Be 850 1:05 17.0 3% 6:4
IP Per 03:37:38.5 +32:22:16 A3 350 0:43 17.0 3% 8:3
MWC 480 04:55:35.5 +29:46:06 A2 140 0:17 17.0 3% 10:3
MWC 297 18:25:01.4 \Gamma03:51:47 O9 450 0:56 16.7 3% 7:4
VV Ser 18:26:14.3 +00:06:40 B9 440 0:54 16.9 3% 7:7
MWC 300 18:26:45.0 \Gamma06:06:48 Be 15500 19 16.3 3% \Gamma0:6
AS 310 18:30:41.7 \Gamma05:00:26 B0 2500 3:09 16.5 3% 3:5
HD 200775 21:00:59.7 +67:57:56 B3 600 0:74 17.0 3% 7:1
V645 Cyg 21:38:10.6 +50:00:43 O7 6000 7:42 17.1 3% 2:2
BD +65 ffi 1637 21:41:41.1 +65:52:49 B2 1000 1:23 17.0 3% 6:0
LkHff 257 21:52:22.8 +46:57:58 B8 900 1:11 17.0 3% 6:2
LkHff 233 22:32:28.3 +40:24:32 A7 880 1:09 17.0 3% 6:3
HD 216629 22:51:18.4 +61:52:46 B2 725 0:90 17.0 3% 6:7
a ) Completness absolute magnitudes have been computed assuming the distance reported in column 5.
tion that Ae stars tend to be closer to the Sun than Be
stars, as expected.
3. Observations and data reduction
The observations of the first sample of 19 sources have
been discussed in Paper I and will not be described again
here. The new 26 stars have been observed during sev­
eral runs at TIRGO (11 fields in J, H and K) and at the
Nordic Optical Telescope (NOT, 15 fields in K only) us­
ing the Arcetri near infrared camera (ARNICA). ARNICA
is equipped with a NICMOS3 256\Theta256 HgCdTe detector
and a complete description of the instrument and its per­
formances at TIRGO can be found in Lisi et al. (1996)
and Hunt et al. (1996). The TIRGO observations were ob­
tained between 1993 and 1996. The observing setup was
the same as in Paper I, with a field of view of ¸ 7 0 \Theta 7 0 for
all objects but Z CMa, for which we covered only an area
of ¸ 4 0 \Theta 4 0 . The ARNICA pixel scale at the TIRGO is
¸ 0:96 00 , which well matches the typical seeing conditions
(2 00 --3 00 ).
The NOT observations were carried out during a five
night run from August 31 st to September 4 th 1996. At
NOT the ARNICA plate scale was 0:52 00 =pix in order to
match the better seeing (in fact, during the whole run the
images have been pixel­limited due to the excellent, sub­
arcsecond, seeing conditions). The field of view of each
image is thus ¸ 2 0 . In order to cover a larger field around
each star, we used a mosaicing technique that yields a
constant signal to noise ratio on a field of ¸ 8:5 0 diameter
centered on the target star; each mosaic consists of at least
42 partially overlapping frames. Flat fielding has been per­
formed using differential flat frames constructed by sub­
tracting one from the other two sky frames at different il­
lumination, obtained by median averaging various sets of
exposures at sunset and sunrise. The differential flat field­
ing was necessary due to the high, spatially non­uniform
emissivity of the telescope (see also Hunt et al. 1996). Af­
ter flat fielding, sky subtraction was performed on each
frame using sky frame obtained by median averaging a
set of exposures in the mosaic, as described in Hunt et
al. (1994). After reduction the images were registered and

L. Testi et al.: A search for clustering around Herbig Ae/Be stars. II 3
Fig. 2. Left: galactic latitude of the observed sources versus spectral type of the Herbig AeBe star. Right: position on the
galactic plane of the observed stars; the position of the Sun is represented by a ``+'' and the Galactic Center is at (0,\Gamma8.5),
filled circles represent stars with spectral type earlier than B8, open circles stars later than B8. The two most distant stars
(MWC 300 and V645 Cyg) are not included. The concentric circles are centered on the Sun position and have radii of 1 and
2 kpc.
Fig. 1. Distribution of the spectral types of 44 of the observed
Herbig AeBe stars (Z CMa, Sp.Type F5, is outside the plot).
combined to form the final large mosaics. All the data
reduction has been performed using the IRAF 1 and AR­
NICA (Hunt et al. 1994) software packages.
1 IRAF is made available to the astronomical community by
the National Optical Astronomy Observatories, which are op­
erated by AURA, Inc., under contract with the U.S. National
Science Foundation
Photometric calibration was performed observing a set
of near infrared photometric standard stars from the AR­
NICA (Hunt et al. 1998) list. The final calibration accu­
racy is ¸ 3% for all fields at the NOT and better than
8% at the TIRGO (except for Z CMa). The calibration
accuracy for each field is reported in Table 1.
As discussed in Paper I, the automatic star finding
algorithms have not proven to be completely reliable in
finding all (and only) the point sources in every field, pri­
marily because of the bright diffuse emission associated
with some of the Herbig AeBe stars. Source lists in all
fields have thus been individually edited and corrected by
inspecting the images at different contrast levels.
Aperture photometry on the detected point sources
was performed using the IRAF DAOPHOT package and
a 4 pixel aperture for both TIRGO and NOT observations,
corresponding to ¸ 4 00 and ¸ 2 00 respectively. The 3oe lim­
iting magnitudes are reported in Table 1. By checking the
cumulative source count plots, we estimate our data to be
complete down to one magnitude brighter than the limit­
ing magnitude of each field. Note that, as in Paper I, the
TIRGO limiting magnitudes refer to the ``edges'' of the
mosaics. Since the fields have not been imaged with con­
stant signal to noise, the central regions of the mosaics are
0:5--1 magnitude deeper.
The completeness absolute magnitude in K (M c
K ) has
been computed from the observed completeness magni­
tude assuming the distance reported in Table 1 (column
11). In computing M c
K , we have neglected the effect of
extinction. We note however that in the K band the cor­
rection due to interstellar extinction is expected to be very

4 L. Testi et al.: A search for clustering around Herbig Ae/Be stars. II
low for all the sources, with the possible exception of the
most distant ones.
4. Results
4.1. Stellar parameters
The properties of 45 observed stars are summarized in
Table 2, which gives an identification number (column 1),
source name (column 2) spectral type (column 3), dis­
tance (column 4), V­magnitude (column 5), (B--V) colour
(column 6), effective temperature T eff (column 7), and
luminosity of the star (column 8). In column 9 we report
the calculated age of the Herbig AeBe star (see Sect. 4.2),
while the minimum mass limits corresponding to 0 and 2
magnitude of extinction in K are given in columns 10--11
(see Sect. 4.3). The stars are listed according to their spec­
tral type, from the earliest to the latest. Spectral types,
distances, V­magnitudes and (B--V) colors are taken from
the literature, as specified in the comments on individual
stars. We determined the effective temperature T eff from
the spectral type, using the scale of Cohen & Kuhi (1979).
The luminosity was then computed by fitting a black­
body of temperature T eff and varying radius to the de­
reddened V­band magnitude and distance. In all cases,
we have assumed a value of the total to selective ex­
tinction RV =3.1. The bolometric corrections are from
Schmidt­Kaler (1981). For variable stars, we have used
the V­magnitude in the brightest state, assuming that the
variability is due to circumstellar extinction.
4.2. Age estimates
The distribution in the H­R diagram of the 39 Her­
big AeBe stars with a determination of temperature and
luminosity is shown in Fig. 3. We have estimated the
stellar ages from their location in the H­R diagram us­
ing the evolutionary tracks and isochrones from Palla &
Stahler (1993). There is a clear distinction between Her­
big AeBe stars of the earliest spectral types (O7 to B5)
and those with types later than B5. For the former an age
estimate based on the H­R diagram is not possible since
they lie either on or above the ZAMS and do not have an
optically visible PMS phase. These stars include number
1 to 14 of Table 2. There are two stars, R Mon (N.4) and
RNO 6 (N.8), which lie far below the ZAMS, in a forbid­
den part of the diagram. This may be to due difficulties
in deriving the correct stellar photometry and reddening
in regions of heavy nebular emission.
Herbig AeBe stars from B5 to A7 are well distributed
at or below the birthline and an age estimate is thus pos­
sible. The individual ages (in million years) are listed in
Table 2 and span a wide range from 0.1 Myr for stars
near the birthline to 10 Myr for LkHff 198, the oldest of
the whole sample. Our age estimates reflect the proce­
dure adopted to compute the stellar parameters and are
subject to several sources of uncertainty. In general, we
Fig. 3. Distribution of 39 Herbig AeBe stars in the H­R dia­
gram. Each star is labeled by its reference number as in Tab. 2.
The solid lines are the evolutionary tracks for M \Lambda =1.5, 2, 2.5,
3, 3.5, 4, 5 and 6 M fi (from bottom to top). The dotted line is
the birthline of Palla & Stahler (1990). The heavy solid line is
the theoretical zero­age main­sequence.
obtain values of the luminosity that are on the low side of
those published in the literature, resulting in greater ages
for the Herbig AeBe stars. In a few cases, the difference
can be quite substantial, up to factors greater than 10.
Examples include LkHff 25, LkHff 198 and LkHff 233. A
possible cause of the discrepancy in luminosity could be
due to our assumption of a single value of R V for all the
stars. In fact, the bolometric luminosity depends sensi­
tively on R V and it is well known that many Herbig AeBe
stars present anomalous extinction, suggesting higher val­
ues of R V than for the standard interstellar case. As an
example, a variation of R V from 3.1 to 5.1 implies an in­
crease of the luminosity of LkHff 198 from ¸10 L fi to ¸45
L fi with a corresponding decrease of age to a more real­
istic value of 1 Myr. Note that a larger value of R V may
also move close to the ZAMS the two stars R Mon and
RNO 6. In principle, a careful analysis of the appropriate
value of R V could be done on each Herbig AeBe star, but
this exercise goes beyond the purpose of this section in
which the stellar ages are only used to obtain the mass
sensitivity limits of our survey, as illustrated in the next
subsection. Moreover, it is important to point out that
the age estimates do not affect the determination of the
clustering properties of Herbig AeBe stars.

L. Testi et al.: A search for clustering around Herbig Ae/Be stars. II 5
Table 2. Star parameters and mass sensitivities
N. Star type D V B­V Log(T) Log(L) age M0 M2 NK I C r c
(pc) (mag) (mag) (K) (L fi ) (Myr) (M fi ) (M fi ) (pc)
1 V645 Cyg O7 6000 13.19 1.07 4.56 5.11 -- -- -- ?5 29.5\Sigma2 0.6
2 MWC 297 O9 450 12.11 2.14 4.52 4.60 -- -- -- 37 20.4\Sigma1 0.05
3 MWC 137 B0 1300 11.93 1.30 4.49 4.48 -- -- -- ?59 76.0\Sigma9 0.4
4 R Mon B0 800 11.92 0.72 4.49 3.34 -- -- -- 0 --12.8\Sigma3 --
5 BHJ 71 B0 730 10.25 0.83 4.49 4.06 -- -- -- 4 4.0\Sigma3 0.15
6 MWC 1080 B0 2500 11.28 1.36 4.49 5.38 -- -- -- ?9 31.0\Sigma3 0.7
7 AS 310 B0 2500 12.39 1.05 4.49 4.55 -- -- -- ?37 70.0\Sigma17 0.4
8 RNO 6 B1 1600 14.52 0.57 4.35 2.34 -- -- -- ?11 11.0\Sigma1 0.3
9 HD 52721 B2 1150 6.38 0.05 4.31 4.53 -- -- -- 10 20.5\Sigma4 0.6
10 BD+65 ffi 1637 B2 1000 10.05 0.42 4.31 3.40 -- -- -- 29 75.0\Sigma5 0.4
11 HD 216629 B2 725 9.25 0.75 4.31 3.85 -- -- -- 29 34.0\Sigma6 0.1
12 BD+40 ffi 4124 B2 1000 10.61 0.79 4.31 3.64 -- -- -- 19 11.0\Sigma3 0.2
13 HD 37490 B3 360 4.50 --0.08 4.25 3.95 -- -- -- 9 9.9\Sigma3 0.14
14 HD 200775 B3 600 7.35 0.42 4.25 3.87 -- -- -- 8 1.9\Sigma1 --
15 MWC 300 Be 15500 -- -- -- -- -- -- -- ?2 21.0\Sigma8 4
16 RNO 1B Be 850 -- -- -- -- -- -- -- 12 9.7\Sigma1 0.15
17 HD 259431 B5 800 8.62 0.27 4.14 3.16 0.05 ! 0:1 ! 0:1 2 0.9\Sigma2 --
18 XY Per B6 160 8.99 0.50 4.11 1.83 2.0 ! 0:1 ! 0:1 3 11.3\Sigma3 0.08
19 LkHff 25 B7 800 12.60 1.18 4.09 2.56 0.2 ! 0:1 0.16 11 14.5\Sigma5 0.3
20 HD 250550 B7 700 9.47 0.07 4.09 2.32 0.5 ! 0:1 0.18 4 2.2\Sigma2 --
21 LkHff 215 B7 800 10.18 0.53 4.09 2.72 0.1 ! 0:1 0.13 7 3.9\Sigma1 0.18
22 LkHff 257 B8 900 13.18 0.78 4.05 1.85 2.0 ! 0:1 0.29 15 5.5\Sigma6 --
23 BD+61 ffi 154 B8 650 10.25 0.59 4.05 2.51 0.1 ! 0:1 ! 0:1 8 --1.4\Sigma3 --
24 VY Mon B8 800 12.84 1.58 4.05 2.88 0.05 ! 0:1 ! 0:1 25 23.2\Sigma5 0.25
25 VV Ser B9 440 11.58 0.97 4.03 2.03 1.0 ! 0:1 ! 0:1 24 16.9\Sigma5 0.1
26 V380 Ori B9 460 10.30 0.56 4.03 2.07 1.0 ! 0:1 ! 0:1 3 --2.0\Sigma2 --
27 V1012 Ori B9 460 -- -- -- -- -- -- -- 4 1.9\Sigma2 --
28 LkHff 218 B9 1150 11.81 0.42 4.03 2.09 1.0 ! 0:1 0.42 8 2.0\Sigma5 --
29 AB Aur A0 160 6.96 0.13 3.99 1.86 1.5 ! 0:1 ! 0:1 ?3 3.0\Sigma6 --
30 VX Cas A0 760 10.94 0.38 3.99 1.94 1.0 ! 0:1 0.11 13 4.5\Sigma4 0.3
31 HD 245185 A2 400 9.85 0.10 3.96 1.34 7.0 ! 0:1 0.17 10 4.5\Sigma5 --
32 MWC 480 A2 140 7.65 0.16 3.96 1.34 7.0 ! 0:1 ! 0:1 ?3 5.0\Sigma6 --
33 UX Ori A2 460 9.70 0.40 3.96 1.89 1.0 ! 0:1 ! 0:1 0 --0.3\Sigma1 --
34 T Ori A3 460 10.15 0.58 3.94 1.89 1.0 ! 0:1 0.10 5 1.0\Sigma2 --
35 IP Per A3 350 10.35 0.41 3.94 1.36 7.0 ! 0:1 0.12 3 5.3\Sigma4 --
36 LkHff 208 A3 1000 11.52 0.48 3.94 1.89 1.0 ! 0:1 0.19 4 2.2\Sigma5 --
37 MWC 758 A3 150 8.31 0.37 3.94 1.39 6.0 ! 0:1 ! 0:1 ?2 3.4\Sigma1 0.03
38 RR Tau A4 800 10.10 0.60 3.93 2.37 0.1 ! 0:1 0.12 7 0.8\Sigma6 --
39 HK Ori A4 460 11.38 0.55 3.93 1.32 7.5 0.11 0.49 7 2.2\Sigma1 --
40 MaC H12 A5 850 -- -- -- -- -- -- -- 15 5.1\Sigma1 0.15
41 LkHff 198 A5 600 13.97 0.97 3.92 0.96 10.0 0.11 0.46 6 --10.6\Sigma11 --
42 Elias 1 A6 160 15.3 1.5 -- -- -- -- -- ?2 2.0\Sigma3 --
43 BF Ori A7 460 9.59 0.26 3.90 1.53 3.0 ! 0:1 0.14 4 1.1\Sigma1 --
44 LkHff 233 A7 880 12.93 0.84 3.90 1.48 4.0 ! 0:1 0.39 2 1.0\Sigma1 --
45 Z CMa F5 1150 8.74 1.29 -- -- -- -- -- ?0 --5.0\Sigma5 --
4.3. Limiting Minimum Mass
Assuming that all the stars located around the Her­
big AeBe star are coeval, it is possible to transform the
K­completeness absolute magnitudes reported in Table 1
into an estimate of the lowest mass detectable in the field,
the so­called minimum mass. For the transformation, we
have used the method discussed in the Appendix (see also
Meyer 1996), which allows one to derive at any given time
a relation between the absolute K­magnitude and the mass
of the star from a set of evolutionary tracks. For consis­
tency, we should have used the same set of tracks em­
ployed for the age estimate. However, the models of Palla
& Stahler (1993) do not extend below 0.6 M fi , whereas
the IR images are deep enough to probe masses near the
brown dwarf limit. Thus, these tracks cannot be used for

6 L. Testi et al.: A search for clustering around Herbig Ae/Be stars. II
the determination of the minimum mass, and we have
used instead the evolutionary tracks of D'Antona & Mazz­
itelli (1994) which extend to substellar masses.
The minimum mass depends on the extinction at K
band. Even though the K extinction is a factor ¸ 10 (in
magnitudes) less than in the visual and the extinction
toward the Herbig AeBe star itself is usually Ÿ 5 mags
in the visual, some of the colour­colour diagrams shown
in the following section reveal that several stars in the
fields are affected by a substantial amount of extinction
(A V ¸ 10 \Gamma 20 mags in some cases). We give in Table 2
the minimum mass in each field for AK = 0 and 2 mags
(Columns 10 and 11). Clearly, the calculation of the mini­
mum mass is possible only for those fields where an age es­
timate of the Herbig AeBe star exists. A value ! 0:1 M fi in
Table 2 means that the mass limit is smaller than the min­
imum mass available from the PMS evolutionary tracks of
D'Antona & Mazzitelli (1994).
Note that the derivation of the minimum mass assumes
that all the observed emission at K­band is due to the stel­
lar photosphere (i.e. the infrared excess is not considered
and corrected for).
4.4. Cluster Indicators
Several methods of measuring the richness of an embedded
cluster of stars associated to the visible Herbig AeBe stars
have been discussed in Paper I. We compute for each of
the observed fields two such indexes, namely NK and I C
which are given in Table 2, Columns 12 and 13.
NK is defined as the number of stars detected in the
K­band image of the field within a distance of 0.21pc
from the Herbig AeBe star with an absolute magnitude
MK !5.2 mag. The first of these two constraints is
set to match the size of the best­studied clusters (e.g.,
BD+40 ffi 4124: Hillenbrand et al. 1995; Palla et al. 1995).
The threshold at MK =5.2 mag is low enough to include
at least some stars in most of the fields. In fact, there are
5 fields (those centered on Elias 1, MWC 758, MWC 480,
AB Aur and XY Per) which have been imaged with a field
of view smaller than 0.21 pc, and 7 (centred on Z CMa,
MWC 300, AS 310, MWC 1080, V 645 Cyg, RNO 6 and
MWC 137) which have M c
K ! 5:2 mag. The values of NK
in Table 2 for these 12 objects should be considered as
lower limits. Note that NK can be directly compared to
the results in Hillenbrand (1995).
The second, more reliable richness indicators is
the quantity I C , which corrects for the ``local'' back­
ground/foreground contamination. I C is computed by in­
tegrating the source surface density profile centered on
the Herbig AeBe star n(r) and by subtracting the average
surface density measured at the edge of each field n1 :
I C =
i max
X
i=0
ú(n(r i ) \Gamma n1 )(r 2
i+1 \Gamma r 2
i ) (1)
where n(r i ) is the local source surface density (i.e. the
number of stars between r i and r i+1 arcsec from the Her­
big AeBe star divided by the area ú(r 2
i+1 \Gamma r 2
i )). i max is
chosen to contain all the members of the cluster and n1
is the mean value of n(r i ) in the outer parts of the plot. In
all fields \Deltar j r i+1 \Gamma r i = 12 00 , which ensures a good ``res­
olution'' and (in most cases) a reasonable number of stars
per annulus. The uncertainty on I C has been computed by
propagating the error in the determination of n1 on the
sum defined in Eq.(1).
The two indexes I C and NK suffer from different biases.
In the case of I C , the main source of errors in compar­
ing values for different fields arises from the fact that all
sources detected within the completeness limit M c
K have
been included, in spite of the fact that M c
K varies from
field to field. A second error derives from possible local
extinction variations within the cluster (note that since
n1 is derived from observations of the same field, line­of­
sight extinction does not affect I C ). This effect leads to a
systematic underestimate of the number of cluster mem­
bers when a compact (with size of the order of the cluster
size), high column density molecular clump is localized at
the position of the Herbig AeBe star. In the case of NK , as
we have already pointed out, the main uncertainty derives
from background/foreground contamination. These points
have been extensively examined in Paper I, and will not
be discussed any further in here.
Both I C and NK are affected by the presence of bright
reflection nebulosities associated to the Herbig AeBe star,
which may ``hide'' low­luminosity companion stars. It is
difficult to quantify this effect. We suggested in Paper I
that it could provide an explanation for the very nega­
tive values of I C in LkHff 198 and R Mon. Among the
new fields observed in this paper, it certainly affects to an
unknown degree the star counts in V645 Cyg.
In the last column of Table 2 we report an estimate
of the stellar group radius, r c , for the fields in which a
source density enhancement is detectable around the Her­
big Ae/Be star. This typical size has been derived as the
radius at which the sources density peak reachs the back­
ground level in the K­band sources surface density profiles
presented below.
5. Comments on individual sources
In the following, we present a brief description of the basic
stellar data for each Herbig AeBe star and of the associ­
ated stellar field. Where available, we also give some infor­
mation about the amount of gas and dust associated with
the stars, since this information will prove useful for the
discussion of the clustering properties of the Herbig AeBe
stars (see Testi et al. 1998). We have recomputed the
mass of circumstellar dust and gas (in units of M fi ) from
the 1.3mm flux as 1:28 \Theta 10 \Gamma4 (D=140pc) 2 F 1:3mm (mJy)
(Natta et al. 1997). Often there are large discrepancies be­
tween the circumstellar masses inferred from millimetric

L. Testi et al.: A search for clustering around Herbig Ae/Be stars. II 7
Fig. 4. V 645 Cyg. Left: K­band image; right: K­band source surface density profile.
Fig. 5. MWC 297. Left: K­band image; right: K­band source surface density profile.
Fig. 6. MWC 137. Top left: J­band image; top right: K­band image; bottom left: colour­colour diagram; bottom right: K­band
source surface density profile.
continuum observations and those derived from molecu­
lar data. Whenever possible, we give both of them. As
in Table 2, the sources are ordered by decreasing spectral
type.
For each Herbig AeBe system observed at TIRGO, we
show the J­ and K­band images, the (J--H,H--K) colour--
colour diagram, and the stellar surface density profile at
K­band. We determine NK and I C and provide an estimate
of the radius of the stellar cluster, when a stellar density
enhancement is present above the background. We have
included the TIRGO observations of the 19 fields analysed
in Paper I since only few fields were shown there. The 1996
NOT observations are limited to the K­band and therefore
we show the K­band image and the corresponding surface
density profile only. White pixels on top of the brighter
stars indicate that these sources are saturated (or fall in
the nonlinear regime of the detector).
For most of the sources observed in the earliest runs
at the TIRGO, the scatter of the points in the colour--
colour diagram is due either to the systematic uncertain­
ties described in Paper I and in Hunt et al. (1996) or to the
unstable atmospheric conditions which appear to plague
more heavily the H­band data. In a few cases (HK Ori,
HD 259431, LkHff 218, HD 245185, and Z CMa) a sys­
tematic offset in the H­band of ¸ 0:2\Gamma0:3 magnitudes is
evident.
5.1. V 645 Cyg (AFGL 2798)
The V­magnitude and (B­V) colour are from Shevchenko
et al. (1993). The distance (6 kpc) and the spectral type
are from Cohen (1977). There is some controversy on the
actual values of the parameters for this star, which some
authors (Goodrich 1986;Hamann & Persson 1992; Corco­
ran & Ray 1998) classify as A0 at distance 3500 pc.
Far­infared studies of this region (Natta et al. 1993)
reveal extended emission at 50 and 100 ¯m, typical of an
extended envelope surrounding the star. The estimated
total mass of the envelope (within 0.5 pc from the star) is
78 M fi . Di Francesco et al. (1997) refer of a possible detec­
tion at 2.7mm with the Plateau de Bure interferometer.
In the radio continuum (3.6 cm; Skinner et al. 1993) the
emission is extended, with an intensity consistent with the
O7 classification of Cohen (1977).
V 645 Cyg is located in a region of extended CO and
NH 3 emission (Torrelles et al. 1983; 1989). Torrelles et
al. (1987) and Verdes­Montenegro et al. (1991) detected
a massive CO outflow associated with the star.
(Fig. 4). The star is embedded in a bright diffuse neb­
ula (see also Goodrich 1986). We detect a group of stars
with a projected radius of ¸ 0:6 pc.
5.2. MWC 297 (SS73 164)
The V­magnitude and (B­V) colour are from Shevchenko
et al. (1993). The distance (450 pc) and the spectral type
(O9) from Hillenbrand et al. (1992).
Hillenbrand et al. (1992) measured a 1.3mm flux of 110
mJy in a region of 0.06pc size, which roughly corresponds
to a circumstellar mass of 0.15 M fi . Mannings (1994) de­
tected the star at all submm wavelengths; the SED is con­
sistent with simple disc emission. However, Di Francesco
et al. (1994) spatially resolve the source, implying contri­
bution from an extended envelope. The molecular survey
of Hillenbrand (1995) yields a mass estimate of M cl =1500
M fi in a region of ¸1 pc in size.
(Fig. 5). Very bright star surrounded by a diffuse neb­
ula. A stellar group is detected with a radius r ¸ 0:05 pc.
5.3. MWC 137 (PK 195\Gamma00.1; PN VV 42)
The V­magnitude and (B­V) colour are from Shevchenko
et al. (1993). The distance (1300 pc) and spectral type
(B0) are from Hillenbrand et al. (1992). There is a big
discrepancy with Berrilli et al. (1992) parameters, but the
latter seem rather uncertain.
The star was once believed to be a planetary nebula
(Perek & Kohoutek 1967; Acker et al. 1987; Acker & Sten­
holm 1990) and its true nature is still disputed. However,
Zijlstra et al. (1990) put it in the list of misclassified plan­
etary nebulae from VLA data: it is shown to be a compact
HII region based on radio morphology, stronger emission
than most Planetary Nebulae and from its location in the
IRAS colour--colour diagram.

8 L. Testi et al.: A search for clustering around Herbig Ae/Be stars. II
Fig. 7. R Mon. Top left: J­band image; top right: K­band image; bottom left: colour­colour diagram; bottom right: K­band
source surface density profile.
Fig. 8. BHJ 71. Top left: J­band image; top right: K­band image; bottom left: colour­colour diagram; bottom right: K­band
source surface density profile.
Fig. 9. MWC 1080. Top left: J­band image; top right: K­band image; bottom left: colour­colour diagram; bottom right:
K­band source surface density profile.
Fig. 10. AS 310. Left: K­band image; right: K­band source surface density profile.
Fig. 11. RNO 6. Top left: J­band image; top right: K­band image; bottom left: colour­colour diagram; bottom right: K­band
source surface density profile.
Fig. 12. HD 52721. Top left: J­band image; top right: K­band image; bottom left: colour­colour diagram; bottom right: K­band
source surface density profile.
Fig. 13. BD +65 ffi 1637. Left: K­band image; right: K­band source surface density profile.
Fig. 14. HD 216629. Left: K­band image; right: K­band source surface density profile.
Fig. 15. BD+40 ffi 4124. Top left: J­band image; top right: K­band image; bottom left: colour­colour diagram; bottom right:
K­band source surface density profile.
Fig. 16. HD 37490. Top left: J­band image; top right: K­band image; bottom left: colour­colour diagram; bottom right: K­band
source surface density profile.
Fig. 17. HD 200775. Left: K­band image; right: K­band source surface density profile.
Fig. 18. MWC 300. Left: K­band image; right: K­band source surface density profile.
Fig. 19. RNO 1B. Left: K­band image; right: K­band source surface density profile.

L. Testi et al.: A search for clustering around Herbig Ae/Be stars. II 9
The far­infrared (FIR) and (sub)mm environment of
this star has been studied extensively in recent years. Di
Francesco et al. (1994) found that the emission at 50 and
100 ¯m peaks on the star but is quite extended. Standard
accretion disks cannot be the sole source of FIR emission
and most of the emission comes from an extended circum­
stellar envelope. The same conclusion is reached through
submm observations by Mannings (1994), who found the
emission at 350 and 450 ¯m to be well in excess of that ex­
pected from an optically thick disk. The star has a 1.3mm
flux of 190 mJy (Hillenbrand et al. 1992), which corre­
sponds to a mass of circumstellar material of about 2 M fi in
a region of 0.18 pc size. Di Francesco et al. (1997) possibly
detect the source at 2.7 mm with the PdB interferometer
giving further support to the hypothesys of the young na­
ture of the object.
The molecular survey of Hillenbrand (1995) yields a
mass estimate of M cl =83 M fi in a region of !0.8 pc
size. Higher resolution observations by Fuente et al. (1998)
show that on a scale of 0.08 pc the amount of gas and dust
is reduced to ¸2 M fi .
(Fig. 6). The Herbig AeBe star is surrounded by a dou­
ble shell like reflection nebulosity. Within the nebula many
faint stars are detected. The source surface density pro­
file clearly shows a peak around MWC 137 with radius
r ¸ 0:4 pc.
5.4. R Mon (BD+08 ffi 1427; MWC 151)
The V­magnitude and (B­V) colour are from Shevchenko
et al. (1993). These estimates may be affected by the
bright nebulosity associated to the star. The distance
(800 pc) is from Finkenzeller & Mundt (1984) and the
spectral type (B0) from Cohen & Kuhi (1979).
Near infrared adaptive optics and visible HST imaging
(Close et al. 1997) reveal a faint companion and resolve
the double helix structure of the diffuse nebulosity. No
other object is found close to the Herbig Be star.
Natta et al. (1993) resolve the 100 ¯m emission associ­
ated to the star and determine an envelope mass ?36 M fi
(within a radius of 0.5 pc). The 1.3mm flux (Hillenbrand
et al. 1992) yields a value of the circumstellar mass in a
region of 0.1 pc size of about 0.4 M fi .
(Fig. 7). The Herbig AeBe star is at the apex of an ex­
tended bright nebulosity. The source density profile shows
a dip around the star position suggesting that background
stars and possibly faint young companions might be hid­
den either by the bright nebula or a molecular clump.
5.5. BHJ 71 (V374 Cep, AS 505)
The V­magnitude and (B­V) colour are from Shevchenko
et al. (1993). The distance (730 pc) is from Berrilli et
al. (1992) and the spectral type (B0) from Finkenzeller
& Mundt (1984).
Both the distance and the spectral classification
are very uncertain. The distance quoted by Berrilli et
al. (1992) is derived assuming that it is a member of the
Cepheus OB3 association.
(Fig. 8). The field is very crowded, a moderate density
enhancement with r ¸ 0:15 pc is marginally detected.
5.6. MWC 1080
The V­magnitude and (B­V) colour are from Shevchenko
et al. (1993). The distance (2500 pc) is from Cant'o et
al. (1984) and the spectral type (B0) from Cohen & Kuhi
(1979).
The uncertainty on the stellar parameters is not large
in this case. Agreement exists in the literature about the
fact that the star is indeed young and a bona fide Her­
big AeBe star. This is supported, among other things
by the detection of a molecular outflow (Levreault 1988)
and high velocity CO line emission (Koo 1989; Wu,
Huang & He 1996). Zinnecker & Preibisch (1994) have de­
tected strong X­ray emission from the object. Leinert et
al. (1997) classify the star as an eclipsing binary and de­
tect an infrared companion at 0.75 00 . The companion ap­
pears to have a high luminosity and could possibly be a
second Herbig AeBe star in the region. This result is con­
firmed by Pirzkal et al. (1997). These findings support the
colliding winds hypothesis for the X­ray emission.
The star is detected at 100¯m by di Francesco et
al. (1994), who derive an apparent size of ¸ 29 00 (corre­
sponding to ¸ 3 \Theta 10 4 AU). The presence of an extended
component is also inferred from the submm observations
of Mannings (1994), who measures 350 and 450¯m flux
densities in excess to the prediction of a simple optically
thick accretion disk model. The source is extended also at
1.3mm. The flux in a 28 00 beam is 540 mJy (Hillenbrand
et al. 1992), which corresponds to about 22 M fi in a re­
gion of about 0.34 pc size. No compact 2.7 mm emission
is detected by di Francesco et al. (1997).
The molecular survey of Hillenbrand (1995) yields a
mass estimate of M cl =1400 M fi in a region of ¸1.1 pc
size. Fuente et al. (1998) have observed the star at the
IRAM­30m telescope and detected emission both in the
line and continuum, obtaining M=11 M fi within 0.08 pc.
On the other hand, Molinari et al. (1996) report no detec­
tion of NH 3 (1,1) and (2,2) line emission and of H 2 O maser
emission.
(Fig. 9). In our NIR images, a conspicuous group of
stars is detected close to the Herbig Be star and embedded
in a diffuse nebulosity. The radius of the group is r ¸
0:7 pc.
5.7. AS 310 (PK 026+01.1; PN VV 425)
The V­magnitude and (B­V) colour are from Shevchenko
et al. (1993). The distance (2500 pc) and the spectral type
(B0) are from Henning et al. (1994).

10 L. Testi et al.: A search for clustering around Herbig Ae/Be stars. II
Fig. 20. HD 259431. Top left: J­band image; top right: K­band image; bottom left: colour­colour diagram; bottom right:
K­band source surface density profile.
Fig. 21. XY Per. Top left: J­band image; top right: K­band image; bottom left: colour­colour diagram; bottom right: K­band
source surface density profile.
The star is associated with the HII region S61
(Georgelin & Georgelin 1970). Henning et al. (1994) ob­
served the source at 1.3 mm and derived a gas mass
of 30 M fi . It is known to be a binary system (Bastian
& Mundt 1979) with separation 4.4 arcsec. Ageorges et
al. (1997) high angular resolution NIR observations have
revealed 4 more sources located close to the binary (all
within 5 00 ) and conclude that there is a small cluster
around the Herbig AeBe star.
AS 310 has a 1.3mm flux of 190 mJy (Henning et
al. 1994), from which we infer a mass of 8 M fi in a re­
gion of 0.28 pc size.
(Fig. 10). In our NIR image the field is extremely
crowded, however a clear peak in the source surface den­
sity profile is seen with a radius of ¸ 0:4 pc. This finding
suggests that Ageorges et al. (1997) are in fact detecting
the brightest (and closer to the Herbig AeBe star) mem­
bers of a conspicuous cluster.
5.8. RNO 6 (HBC 334; IRAS 02130+5509)
The star is from the Red and Nebulous Objects cata­
logue of Cohen (1980), who give the spectral type that
we are using (B1). The distance (1600 pc) is from Scar­
rot et al. (1986). V and (B­V) from Herbig & Bell (1988)
catalogue. It is not included in the list of Finkenzeller &
Mundt (1984).
(Fig. 11). An arc­shaped nebula is detected at all NIR
wavelegths. The source surface density profile shows a
clear enhancement toward the central position. The ra­
dius of the density peak is r ¸ 0:3pc.
5.9. HD 52721 (BD\Gamma11 ffi 1747; MWC 164;
IRAS 06594\Gamma1113; GU CMa; VDB 88)
The V­magnitude and (B­V) colour are from Shevchenko
et al. (1993). The distance (1150 pc) is from Finkenzeller
& Mundt (1984) and the spectral type (B2) from Hillen­
brand et al. (1992).
New spectroscopic results (van den Ancker et al. 1997)
confirm that the spectral type is B2Ve. Evidence from ro­
tational velocity and the small IR excess supports the in­
terpretation that it could be a classical Be star rather than
a Herbig Be star. However, we detect a measurable excess
of stars around it (Paper I) supporting the hypothesis that
it is indeed a young star surrounded by a group of lower
luminosity objects. The estimate of the distance (1150 pc)
comes from Herbst (1982) who assumed that the star is at
the same distance of the nebulosity of CMa R1.
Fuente et al. (1998) have observed this object at mm
wavelengths; they find that the star sits in a large cavity
devoid of molecular gas.
(Fig. 12). Very crowded field with a marginally de­
tected source enhancement with radius r ¸ 0:6 pc.
5.10. BD +65 ffi 1637 (NGC 7129; V361 Cep; HBC 730;
AS 475)
The V­magnitude, (B­V) colour and spectral type (B2)
are from Shevchenko et al. (1993). The distance (1 kpc) is
from Finkenzeller & Mundt (1984).
This star is in the same molecular complex that har­
bors LkHff 234. Large scale observations of the molecular
emission have shown that BD +65 ffi 1637 (and most of the
cluster, see below) are at the center of a region evacuated
from the molecular material, while LkHff 234 is at the
edge of a molecular ridge (Fuente et al. 1998). From line
and continuum measurements the mass of gas and dust as­
sociated with the star is very modest (M13 CO = 0:4 M fi ,
MCS = 1:0 M fi , M dust = 0:6 M fi ).
(Fig. 13). A clear enhancement of stars is detected be­
tween the two Herbig AeBe stars BD +65 ffi 1637 (the more
massive visible star in the region) and LkHff 234, the
brightest source in the field at K­band, located toward
the north east with respect to the center. The peak of
the stellar surface density profile centered on the B2 star
has a radius of ¸ 0:4 pc. Diffuse emission is clearly de­
tected around LkHff 234 and in a ¸ 2 arcminute long fila­
ment, which is probably marking the interaction between
the radiation field of BD +65 ffi 1637 and the surface of the
molecular cloud that sorrounds the stellar group toward
the south east. The large scale molecular observations of
Fuente et al. (1998) confirmed that this structure is indeed
tracing the edge of the molecular cloud.
5.11. HD 216629 (BD+61 ffi 2361; MWC 1075; IL Cep)
The V­magnitude and (B­V) colour are from Shevchenko
et al. (1993). The distance (725 pc) is from Gar­
many (1973) and the spectral type that we assume (B2)
is from Finkenzeller & Mundt (1984).

L. Testi et al.: A search for clustering around Herbig Ae/Be stars. II 11
Fig. 22. LkHff 25. Top left: J­band image; top right: K­band image; bottom left: colour­colour diagram; bottom right: K­band
source surface density profile.
Fig. 23. HD 250550. Top left: J­band image; top right: K­band image; bottom left: colour­colour diagram; bottom right:
K­band source surface density profile.
Fig. 24. LkHff 215. Top left: J­band image; top right: K­band image; bottom left: colour­colour diagram; bottom right: K­band
source surface density profile.
The NIR images of Pirzkal et al. (1997) reveal a com­
panion at 6.96'' with no difference at K between the pri­
mary and the companion star.
(Fig. 14). Very crowded field with a moderate source
surface density enhancement with r ¸ 0:1 pc detected.
The bright companion detected by Pirzkal et al. (1997) is
clearly revealed.
5.12. BD+40 ffi 4124 (MWC 340; V 1685 Cyg; He 3­1882)
The V­magnitude and (B­V) colour are from Shevchenko
et al. (1993). The distance (1000 pc) and spectral type
(B2) from Finkenzeller & Mundt (1984).
The object is detected at 1.3mm (Hillenbrand et
al. 1992); the corresponding circumstellar mass is about
1.5 M fi in a region of 0.14 pc size. In the 2.7 mm ob­
servations of di Francesco et al. (1997) the star itself is
not detected. However, they detect a strong, unresolved
source 0.9'' north of V1318 Cyg S. This source is also
closest to the emission peak at 800 ¯m (Aspin, Sandell &
Weintraub 1994), and the center of the outflow and H 2 O
maser emission (Palla et al. 1995), and it is believed to be
one of the youngest sources in the region.
The molecular survey of Hillenbrand (1995) yields a
mass estimate of M cl =862 M fi in a region of =0.7 pc
size.
(Fig. 15). An embedded rich group is detected within
r ¸ 0:2 pc from the Herbig Be star, embedded in a diffuse
nebulosity. There are at least three bright members in the
group at K­band. This region has been studied in detail
by Aspin et al. 1994, Hillenbrand et al. 1995 and Palla et
al. 1995. The group is embedded in a compact molecular
clump which prevents the detection of at least 70% of the
sources at optical (R) wavelengths.
5.13. HD 37490 (! Ori; MWC 117; BD+04 ffi 1002;
HR 1934; IRAS 05365+0405; SAO 113001;
HIP 26594)
The V­magnitude and (B­V) colour are from Berrilli et
al. (1992), the distance (360 pc) from Racine (1968), spec­
tral type (B3) from Finkenzeller & Mundt (1984).
Hillenbrand et al. (1992) give a distance of 360 pc and
a spectral type B2; from the shape of the SED they clas­
sify it as a Group III Herbig AeBe star. Hipparcos mea­
surements (van den Anker et al. 1998) give a parallax of
2\Sigma0:9 mas and a distance ? 210 pc.
(Fig. 16). The bright Herbig AeBe star is surrounded
by a faint nebulosity. A stellar density enhancement with
radius r ¸ 0:14 pc is detected.
5.14. HD 200775 (BD+67 ffi 1283; MWC 361; HBC 726)
The V­magnitude and (B­V) colour are from Shevchenko
et al. (1993). The distance (600 pc) and the spectral type
(B3) are from Finkenzeller & Mundt (1984).
The molecular survey of Hillenbrand (1995) yields a
mass estimate of M cl =720 M fi in a region of ¸0.8 pc
size. High resolution observations by Fuente et al. (1998)
show that on a scale of 0.08 pc the amount of gas and dust
is reduced to ¸1.5 M fi .
(Fig. 17). The star is surrounded by a bright nebulos­
ity, which is probably marking the region where the stellar
radiation field interacts with the surrounding molecular
material. No source surface density enhancement is de­
tected.
5.15. MWC 300 (V431 Sct; IRAS 18267\Gamma0606;
HBC 283; HIP 90617)
Both the distance and the spectral classification are very
uncertain. We take a distance of 15.5 kpc and a spectral
type Be, as reported by Leinert et al. (1997).
(Fig. 18). Our image shows a very crowded field, a stel­
lar density peak with radius r ¸ 4 pc (assuming a distance
of 15.5 kpc) is possibly detected.

12 L. Testi et al.: A search for clustering around Herbig Ae/Be stars. II
Fig. 25. LkHff 257. Left: K­band image; right: K­band source surface density profile.
Fig. 26. BD+61 ffi 154. Top left: J­band image; top right: K­band image; bottom left: colour­colour diagram; bottom right:
K­band source surface density profile.
Fig. 27. VY Mon. Top left: J­band image; top right: K­band image; bottom left: colour­colour diagram; bottom right: K­band
source surface density profile.
5.16. RNO 1B
Yang et al. (1991) classify this star as a FU Orionis star,
the distance is estimated to be 850 pc. The spectral classi­
fication is very uncertain (Be­type). The infrared source is
coincident with an ammonia clump (Estarella et al. 1993)
with a size of 0:5 \Theta 0:2 pc and an estimated H 2 column
density of 10 23 cm \Gamma2 . Anglada et al. (1994) report the
detection of a group of compact radio sources, none of
which is coincident with RNO 1B or RNO 1C, which are
the brightest objects at 2.2¯m
(Fig. 19). The star is surrounded by a bright extended
nebulosity. Within the nebula a small group of stars with
r ¸ 0:15 pc is detected. The field stars surface density
appears to increase away from the Herbig AeBe star, sug­
gesting that localized extinction is present. The size of the
cluster appears to be consistent with that of the ammo­
nia clump detected by Estarella et al. 1993). The presence
of localized dense molecular material could explain the
lack of background stars close to the central object. How­
ever, the expected extinction provided by the molecular
gas would prevent the detection of young stars embebbed
inside the clump, thus the most plausible explanation is
that a cluster of young stars is emerging from the ob­
server's side of the cloud.
5.17. HD 259431 (BD+10 ffi 1172; MWC 147; NGC 2247)
The V­magnitude and (B­V) colour are from Shevchenko
et al. (1993). The distance (800 pc) is from Finkenzeller
& Mundt (1984) and the spectral type (B5) from Hillen­
brand (1995).
The star is included in the Hipparcos data (van den
Ancker 1998), however, only a lower limit to the distance
(D?130 pc) is given. It is classified as a B1Ve star (with
Log T eff =4.41 K) in Monoceros (associated with L 1605,
NGC 2247 and Mon R1).
The molecular survey of Hillenbrand (1995) yields a
mass estimate of M cl =480 M fi in a region of =0.8 pc
size.
(Fig. 20). In our images the star appears to be isolated
and surrounded by a faint infrared nebulosity.
5.18. XY Per (HD 275877; ADS 2788; BD+38 ffi 811)
The V­magnitude and (B­V) colour are from Shevchenko
et al. (1993). The distance (160 pc) is from Cohen (1973),
and the spectral type (B6) from Finkenzeller &
Mundt (1984). The distance is uncertain. Hipparcos data
(van den Ancker et al. 1998) give a distance of 120 +88
\Gamma36 pc,
A2II+B6e, Log(T eff )=4.15. NIR shift­and­add imaging
finds a companion at 1.2'' (192 AU at the assumed dis­
tance) with no K magnitude difference between primary
and companion (Pirzkal et al. 1997).
(Fig. 21). Although the field does not appear to be
crowded, the source surface density profile reveals only a
moderate enhancement of sources within r ¸ 0:08 pc from
the Herbig AeBe star.
5.19. LkHff 25 (HBC 219; V590 Mon;
IRAS 06379+0950)
The V­magnitude and (B­V) colour are from Shevchenko
et al. (1993). The distance (800 pc) is from Finkenzeller
& Mundt (1984) and the spectral type (B7) from Hillen­
brand (1995). Hillenbrand et al. (1992) classify this star as
a Group II star, and spectral type A0, while Finkenzeller
& Mundt (1984) classify it as a B8 star.
(Fig. 22). Crowded field with several bright stars and
faint diffuse nebulosity. A small group of stars is detected
within r ¸ 0:3 pc from the Herbig AeBe star.
5.20. HD 250550 (BD+16 ffi 974; MWC 789)
The V­magnitude and (B­V) colour are from Shevchenko
et al. (1993). The distance (700 pc) is from Finkenzeller
& Mundt (1984), the spectral type (B7) from Hillenbrand
et al. (1992).
The star is included in the Hipparcos data of van den
Ancker et al. (1998), but only a lower limit to the distance
(?110 pc) is given.
The star is not detected at 1.3mm (Hillenbrand et
al. 1992); the corresponding upper limit on the circumstel­
lar mass is 0.13 M fi in a region of 0.1 pc size. The molecu­
lar survey of Hillenbrand (1995) yields a mass estimate of

L. Testi et al.: A search for clustering around Herbig Ae/Be stars. II 13
Fig. 28. VV Ser. Left: K­band image; right: K­band source surface density profile.
Fig. 29. V 380 Ori. Top left: J­band image; top right: K­band image; bottom left: colour­colour diagram; bottom right: K­band
source surface density profile.
Fig. 30. V 1012 Ori. Top left: J­band image; top right: K­band image; bottom left: colour­colour diagram; bottom right:
K­band source surface density profile.
M cl =140 M fi in a region of 0.5 pc size. Higher resolution
observations by Fuente et al. (1998) show that on a scale
of 0.08 pc the amount of gas and dust is reduced to ¸5
M fi .
(Fig. 23). Close to the bright Herbig AeBe star there
is a faint nebulosity to the north. No source density en­
hancement is detected.
5.21. LkHff 215 (NGC 2245)
The V­magnitude and (B­V) colour are from Shevchenko
et al. (1993). The distance (800 pc) and spectral type (B7)
from Finkenzeller & Mundt (1984).
Detected at submm wavelengths by Mannings (1994),
who concluded from modelling of the SED that a second
dust component in addition to an optically thick disk is
required to explain the excess of emission at 450 ¯m.
The molecular survey of Hillenbrand (1995) yields a
mass estimate of M cl = 312 M fi in a region of 0.5 pc
size. Higher resolution observations by Fuente et al. (1998)
show that on a scale of 0.08 pc the amount of gas and dust
is reduced to ¸4 M fi .
(Fig. 24). A small group of stars is detected within
r ¸ 0:18 pc from the Herbig AeBe star. The group is em­
bedded in an arc shaped nebulosity.
5.22. LkHff 257 (HBC 312; IRAS 21523+4657)
The V­magnitude and (B­V) colour are from Shevchenko
et al. (1993). The distance (800 pc) and the spectral type
(B8) are from Damiani et al. (1994).
Li et al. (1994) observed this source but reported no
detection of companions or extended infrared emission.
(Fig. 25). In our large field infrared image, the stars in
the field appear unevenly distributed, but no clear central
peak is revealed in the source surface density profile.
5.23. BD+61 ffi 154 (V594 Cas; IRAS 00403+6138;
MWC 419; HIP 3401; HBC 330)
The V­magnitude and (B­V) colour are from Shevchenko
et al. (1993). Distance (650 pc) and spectral type (B8) are
from Finkenzeller & Mundt (1984). The Hipparcos paral­
lax of 3:3 \Sigma 1:6 mas (van den Anker 1998) yields a lower
limit on the distance of D? 120 pc (which is consistent
with the distance that we assume).
Hillenbrand et al. (1992) classify this as a Group I star.
Li et al. (1994) observed the source to search for faint
companions but their NIR images did not revealed any
close companion or extended emission.
Millimeter observations by Hillenbrand et al. (1992)
give a mass of about 0.16 M fi in a region of about 0.1 pc
size. The molecular survey of Hillenbrand (1995) yields an
upper limit to the total mass of M cl !180 M fi in a region
of 0.2 pc size. Higher resolution observations by Fuente et
al. (1998) show that on a scale of 0.08 pc the amount of
gas and dust is reduced to ¸1 M fi .
(Fig. 26). The source surface density is uniform across
the field (within the uncertainties), no density enhance­
ment is detected around the Herbig AeBe star.
5.24. VY Mon (HBC 202; IC 446)
The V­magnitude and (B­V) colour are from Shevchenko
et al. (1993). The distance and spectral type that we adopt
are from Damiani et al. (1994). The distance is that of the
Monoceros OB1 association of which the star is assumed
to be a member. The spectral type (B8) is from Th'e et
al. (1994).
(Fig. 27). A small group of stars within r ¸ 0:25 pc is
detected around the Herbig AeBe star. Some of the stars
in the field show infrared excess and a consistent amount
of extinction.
5.25. VV Ser (HBC 282; IRAS 18262+0006)
The V­magnitude and (B­V) colour are from Shevchenko
et al. (1993). The distance (440 pc) and the spectral type
(B9) that we assume are from Hillenbrand et al. (1992).
However, spectral type (and distance) are rather uncer­
tain. Finkenzeller & Mundt (1984) give B1/B3; Hamann
& Persson (1992) B5; Chavarria­K et al. (1988) A2 and
240 pc. All these different classifications are based on spec­
tra, but use different lines.

14 L. Testi et al.: A search for clustering around Herbig Ae/Be stars. II
Fig. 31. LkHff 218. Top left: J­band image; top right: K­band image; bottom left: colour­colour diagram; bottom right: K­band
source surface density profile.
Fig. 32. AB Aur. Top left: J­band image; top right: K­band image; bottom left: colour­colour diagram; bottom right: K­band
source surface density profile.
Fig. 33. VX Cas. Left: K­band image; right: K­band source surface density profile.
Li et al. (1994) observed the source in their NIR survey
for faint companions. In the H­band contour plot that they
show there are 6 stars within ¸ 15 00 from the Herbig AeBe
star. However, in spite of the fact that the closest compan­
ion is at ¸ 3350 AU from the star, it is not detected in the
search for close companions of Leinert et al. (1997), which
should include all companions closer than 3600 AU.
The star is not detected in the millimeter (Hillenbrand
et al. 1992). An estimate of the mass within 0.03 pc gives
! 0:025 M fi (Natta et al. 1997).
(Fig. 28). Our K­band image is completely consistent
with the images of Li et al.( 1994), and we detect all their
six sources. A clear source surface density enhancement is
detected around the star with r ¸ 0:1 pc.
5.26. V380 Ori (BD\Gamma06 ffi 1253; MWC 765; Haro 4­235)
The V­magnitude and (B­V) colour are from Shevchenko
et al. (1993). The distance (460 pc) and spectral type (B9)
from Hillenbrand et al. (1992).
The Hipparcos parallax (van den Ancker et al. 1998) is
not determined with sufficient accuracy to derive a reliable
estimate of the distance of the object.
In their survey, Leinert et al. (1997) find a companion
at 0.134'' (71 AU) with a luminosity of ¸50 L fi (corre­
sponding to another young intermediate mass star in the
region)
There is a weak 1.3mm emission associated to this star
(Henning et al. 1994); the corresponding amount of cir­
cumstellar gas and dust is rather small (0.01 M fi in a re­
gion of 0.05 pc size).
(Fig. 29). The Herbig AeBe star is surrounded by a dif­
fuse nebulosity, which might prevent the detection of faint
companions close to the star. The source surface density
profile does not show any enhancement close to the cen­
tral position. Many NIR excess and reddened stars are
detected in the field.
5.27. V 1012 Ori (HBC 431; IRAS 05090\Gamma0226)
To our knowledge, there is no measurements of V and
(B­V) in the literature, hence it has not been possible
to derive the stellar parameters as described above. The
distance (460 pc) and spectral type (B9) are from Herbig
& Bell (1988) catalogue.
(Fig. 30). Very few stars in the field, no group detected.
5.28. LkHff 218
The V­magnitude and (B­V) colour are from Shevchenko
et al. (1993). The distance (1150 pc) is from Herbst et
al. (1982) and spectral type (B9) from Hillenbrand et
al. (1992).
(Fig. 31). Crowded field, no stellar density enhance­
ment detected.
5.29. AB Aur (HD 31293;BD+30 ffi 741; MWC 93)
The V­magnitude and (B­V) colour are from Shevchenko
et al. (1993). The distance (160 pc) from Finkenzeller
& Mundt (1984), the spectral type (A0) from Cohen &
Kuhi (1979).
The distance and physical parameters that we
adopt are in agreement with the Hipparcos estimates:
d=144 pc, Spectral type A0Ve+sh, Log(T eff )=4.00,
Log(L)=1.72 L fi (van den Ancker 1997).
AB Aur is not resolved at 50 and 100 ¯m by Di
Francesco et al. (1994). It is detected (Mannings 1994) at
all submm wavelengths; from the 1.3mm flux in a FWHM
beam of 28 00 (Hillenbrand et al. 1992), Natta et al. (1997)
derive a circumstellar mass of 0.013 M fi . Most of the
matter is likely to be in a circumstellar disk, detected at
2.3mm with the OVRO interferometer (Mannings & Sar­
gent 1997).
(Fig. 32). AB Aur is an isolated very bright star with
an extended halo detected in all our images.
5.30. VX Cas (HBC 329; IRAS 00286+6142)
The V­magnitude, (B­V) colour and the spectral type
(A0) are from Shevchenko et al. (1993). The distance
(760 pc) is from Natta et al. (1997).
The star is not detected at 1.3mm (Natta et al. 1997;
F 1:3mm !6 mJy).

L. Testi et al.: A search for clustering around Herbig Ae/Be stars. II 15
Fig. 34. HD 245185. Top left: J­band image; top right: K­band image; bottom left: colour­colour diagram; bottom right:
K­band source surface density profile.
Fig. 35. MWC 480. Left: K­band image; right: K­band source surface density profile.
Fig. 36. UX Ori. Top left: J­band image; top right: K­band image; bottom left: colour­colour diagram; bottom right: K­band
source surface density profile.
(Fig. 33). Rather crowded field, a moderate density
enhancement is detected around the Herbig AeBe star
within r ¸ 0:3 pc.
5.31. HD 245185 (V1271 Ori; BD+09 ffi 880; HBC 451;
IRAS 05324+0959)
The V­magnitude and (B­V) colour are from Shevchenko
et al. (1993). The spectral type (A2) and distance (400 pc)
that we assume is that of Hillenbrand et al. (1992).
Mannings (1994) reports a single­dish 1.3mm flux of
44 mJy for this source, which corresponds to about 0.05
M fi . The star has also been detected in the 2.7 mm con­
tinuum by Mannings & Sargent (1997) with the OVRO
interferometer, but not in the CO(1\Gamma0) line.
(Fig. 34). In our NIR images the field appears to be
very crowded but without a clear density enhancement
around the Herbig AeBe star.
5.32. MWC 480 (HD 31648; HIP 23143; BD+29 ffi 774)
The V­magnitude and the (B­V) colour are from the Hip­
parcos catalogue (van den Ancker et al. 1998). The dis­
tance (140 pc) and the spectral type (A2) are from Man­
nings, Koerner & Sargent (1997).
The Hipparcos parallax give an estimate of the dis­
tance consistent with what we assume (131 pc).
Mannings & Sargent (1997) quote a single­dish 1.3mm
flux of 360 mJy, from which we estimate a mass of cir­
cumstellar gas and dust of the order of 0.05 M fi . They
detect a compact continuum emission at 2.6mm and CO
source with the OVRO interferometer, that they inter­
pret as evidence of a circumstellar disk. The presence of
a circumstellar rotating gaseous disk is confirmed by the
observations of Mannings, Koerner & Sargent (1997)
(Fig. 35). No clear source surface density enhancement
is detected.
5.33. UX Ori (HD 293782; BD\Gamma04 ffi 1029;
IRAS 05020\Gamma0351; HBC 430)
The V­magnitude and (B­V) colour are from Shevchenko
et al. (1993). The distance (460 pc) and spectral type (A2)
are from Hillenbrand et al. (1992).
Hipparcos data (van den Ancker 1998) give d?130 pc,
AIIIe, Log(T eff )=3.93 K, Log(L)?0.40 L fi , which are
consistent with what we assume.
The star is detected at 1.3mm by Natta et al. (1997),
who measure a mass 0.03 M fi in a region of size 0.02 pc.
(Fig. 36). Rather empty field, no density enhancement
detected around the Herbig AeBe star.
5.34. T Ori (BD\Gamma05 ffi 1329; MWC 763; Haro 4­123;
NGC 1977 884)
The V­magnitude and (B­V) colour are from Shevchenko
et al. (1993). The distance (460 pc) is from Hillenbrand et
al. (1992) and spectral type that we adopt (A2) from Hil­
lenbrand (1995); however, Hillenbrand et al. (1992) give
B9, whereas Finkenzeller & Mundt (1984) give A3.
It is known as an eclipsing and spectroscopy bi­
nary with a period of 14.3 days (Shevchenko & Vit­
richenko 1994); Hillenbrand (1995) finds a companion at
2.2 ¯m 7.7'' away (3500 AU) (confirmed by Leinert et
al. 1997), however, due to the high stellar enhancement
of the field it is unclear whether it is a real companion;
its estimated luminosity is ¸2 L fi (typical of a low mass
TTauri star).
Henning et al. (1994) measure a 1.3mm flux of 88 mJy
with a beam of 23 00 , which corresponds to 0.12 M fi within
a radius of 0.025 pc (Natta et al. 1997).
(Fig. 37). Large scale extended emission is clearly de­
tected in all the NIR bands. There seems to be a gen­
eral tendency of a higher stellar density toward the north­
west of the Herbig AeBe star, however no clear density
enhancement is detected around it.

16 L. Testi et al.: A search for clustering around Herbig Ae/Be stars. II
5.35. IP Per (HD 278937; HBC 348; BD+32 ffi 656;
IRAS 03376+3222)
The V­magnitude, (B­V) colour and spectral type (A3)
are from Herbig & Bell (1988). The distance of 350 pc
attributed to this star assumes that it is a member of
the Perseus I OB association (Wood, Myers & Daugh­
erty 1994).
(Fig. 38). Rather empty field, no stellar group is de­
tected around the Herbig AeBe star.
5.36. LkHff 208 (NGC 2163)
The V­magnitude and (B­V) colour are from Shevchenko
et al. (1993). Both the distance (1000 pc) and the spec­
tral type (A3) that we adopt are from Hillenbrand et
al. (1992).
Leinert et al. (1997) found a comparatively close
binary with a separation of 0.115 00 (corresponding to
115 AU); its luminosity appears high (¸100 L fi ) but
rather uncertain.
Millimeter observations (Natta et al. 1997) give an up­
per limit to the circumstellar mass ! 0:03 M fi within 0.025
pc. However, the molecular survey of Hillenbrand (1995)
yields a mass estimate of M cl =640 M fi in a region of ¸0.8
pc size.
(Fig. 39). The stellar surface density appears to be con­
stant across the whole field. A number of stars show a con­
sistent amount of extinction (as seen from the (J--H,H--K)
colour­colour diagram).
5.37. MWC 758 (HD 36112; BD+25 ffi 843;
IRAS 05273+2517; HIP 25793)
The V­magnitude and the (B­V) colour are from the
Hipparcos catalogue (van den Ancker et al. 1998). The
distance and spectral type that we adopt are those re­
ported by Mannings & Sargent (1997), who give A5 and
D= 150 pc.
Mannings & Sargent (1997) quote a single­dish 1.3mm
flux of 72 mJy, which corresponds to 0.01 M fi of circum­
stellar gas and dust; their OVRO observations also detect
compact continuum and CO emission which is likely to
come from a circumstellar disk.
(Fig. 40). A stellar surface density enhancement with
r ¸ 0:03 pc is marginally detected.
5.38. RR Tau (BD+26 ffi 887a; HD 245906;
IRAS 05363+2620; HBC 170; AS 103)
The V­magnitude and (B­V) colour are from Shevchenko
et al. (1993). The distance (800 pc) is from Finkenzeller
& Mundt (1984) and the spectral type (A4) from Hillen­
brand et al. (1992).
Millimeter continuum observations (Henning et
al. 1994) give only an upper limit to the amount of cir­
cumstellar matter in the immediate surroundings of the
star (!0.03 M fi within a distance of 0.05 pc). However,
the molecular survey of Hillenbrand (1995) yields a mass
estimate of M cl =240 M fi in a region of ¸1.6 pc size.
(Fig. 41). In our NIR images, the field appears to be
rather crowded, with no density enhancement.
5.39. HK Ori (MWC 497; MHff 265­13)
The V­magnitude and (B­V) colour are from Shevchenko
et al. (1993). The distance (460 pc) from Hillenbrand et
al. (1992) and spectral type (A4) from Finkenzeller &
Mundt (1984).
K­band speckle interferometry (Leinert et al. 1997) re­
veals a companion at 0.34 00 (156 AU), which is probably
a low mass young star.
There is no molecular gas left around HK Ori. Fuente
et al. (1998) did not detect 13 CO and CS emission, while
1.3 mm continuum observations provide an upper limit to
the dust mass of !0.5 M fi within 0.08 pc.
(Fig. 42). Our NIR observations are affected by large
photometric uncertainties (see Paper I). No clear density
enhancement detected around the star. The colour­colour
diagram reveals a probable systematic offset in the pho­
tometry.
5.40. MaC H12 (HBC 1; PP 1)
The distance (850 pc) and the spectral type (A5) that we
adopt are from Cohen & Kuhi (1976).
Osterloh & Beckwith (1995) detect the source at
1.3mm; from their 1.3mm flux, we derive a mass of cir­
cumstellar matter of 0.2 M fi in a region of 0.04 pc size.
(Fig. 43). Moderately crowded field, a small group of
stars is marginally detected within r ¸ 0:15 pc from the
Herbig AeBe star.
5.41. LkHff 198 (V633 Cas)
The V­magnitude and (B­V) colour that we use are from
Shevchenko et al. (1993). The distance (600 pc) is from
Chavarria­K. (1985), and the spectral type (A5) from Hil­
lenbrand et al. (1992).
The mid­infrared companion found by Lagage et
al. (1993) at 10 ¯m 6 00 north of the optical source is also
detected in the NIR (Li et al. 1994; Leinert et al. 1997).
The projected separation of the binary is 3300 AU; the
estimated luminosity of the companion is ¸100 L fi , thus
it could be the third Herbig AeBe star in the system.
Natta et al. (1993), from 50 and 100 ¯m observations,
infer the existence of a dusty envelope surrounding the
star, with a mass of about 45 M fi within 0.5 pc. Mil­
limeter observations at 1.3mm (Hillenbrand et al. 1992)
and 2.7mm (Di Francesco et al. 1997) reveal an extended
source; the mass of dust and gas in a region of size
0.08 pc is about 1 M fi . The molecular survey of Hillen­
brand (1995) yields a mass estimate of M cl =373 M fi in
a region of 0.4 pc size. Higher resolution observations by

L. Testi et al.: A search for clustering around Herbig Ae/Be stars. II 17
Fig. 37. T Ori. Top left: J­band image; top right: K­band image; bottom left: colour­colour diagram; bottom right: K­band
source surface density profile.
Fig. 38. IP Per. Left: K­band image; right: K­band source surface density profile.
Fig. 39. LkHff 208. Top left: J­band image; top right: K­band image; bottom left: colour­colour diagram; bottom right: K­band
source surface density profile.
Fuente et al. (1998) show that on a scale of 0.08 pc the
amount of gas and dust is reduced to ¸5 M fi .
(Fig. 44). The two bright Herbig AeBe stars LkHff 198
and V 376 Cas are embedded in a diffuse nebulosity de­
tected in all the three NIR bands. Faint sources close
to the bright stars are difficult to detect within the ex­
tended emission. The K­band source surface density in­
creases away from the central stars, suggesting that ei­
ther the diffuse emission or the increased extinction due
to a compact molecular clump localized around the Her­
big AeBe stars prevent the detection of background stars
and, possibly, faint companions.
Support to this possibility comes from the submm con­
tinuum observations of Sandell & Weintraub (1994) who
found an embedded source at the center of a molecular
outflow. 2.7 mm observations of Di Francesco et al. (1997)
indicate that this source is quite extended and may thus
provide a substantial amount of spatially extended extinc­
tion.
5.42. Elias 1 (V892 Tau)
The V­magnitude and (B­V) colour are from Berrilli et
al. (1992), the distance (160 pc) and spectral type (A6)
are from Hillenbrand (1995).
Pirzkal et al. (1997) NIR imaging reveals a companion
at 3.72'' (595 AU) with a K mag difference of 4.2 between
primary and companion. The companion is also revealed
in the speckle interferometry survey for binaries among
Herbig AeBe stars of Leinert et al. (1997); they give the
IR companion position 4'' (570AU) to the NE of the target
star, fainter by 4­5 mag; its estimated luminosity is 0.4 L fi .
It is also detected in the radio continuum survey of Skinner
et al. 1993, who agree that it is probably a low mass pre­
main sequence star.
Hillenbrand et al. (1992) measure a 1.3mm flux of 490
mJy with a beam FWHM of 28 00 , which corresponds ap­
proximately to 0.08 M fi of dust and gas in a region of
0.02 pc size. Di Francesco et al. (1997) detect the star at
2.7 mm with the PdB interferometer within 1 00 of the op­
tical position.
(Fig. 45). Our NIR images show an almost empty field,
with no stellar density enhancement detected. In our im­
ages the faint companion is completely hidden by the lu­
minosity of the Herbig AeBe star.
5.43. BF Ori (BD\Gamma06 ffi 06 1259; HBC 169;
IRAS 05348\Gamma0636; Haro 4­229)
The V­magnitude and (B­V) colour are from Shevchenko
et al. (1993). The distance (460 pc) is from Hillenbrand
et al. (1992) and the spectral type (A7) from Hillen­
brand (1995); however, Hillenbrand et al. (1992) give F2,
whereas Finkenzeller & Mundt (1984) give A/F. We de­
cided to adopt A7 which represent a mean value of the
various determinations.
Hipparcos data (van
den Ancker 1998) give: ú=\Gamma0.7 mas, d?210 pc, A5­6IIIe,
Log(T eff )=3.90 K, Log(L)?0.56 L fi , consistent with our
assumptions.
BF Ori is detected at 1.3mm by Natta et al. (1997),
who estimate a total mass of 0.008 M fi in a region of 0.05
pc size.
(Fig. 46). No clear density enhancement is detected,
even though the brightest sources are located near the
Herbig AeBe star.
5.44. LkHff 233 (V 375 Lac; HBC 313)
The V­magnitude and (B­V) colour are from Shevchenko
et al. (1993). The distance (880 pc) and the spectral type
(A7) are from Finkenzeller & Mundt (1984).
The star is not detected at 1.3mm (! 40 mJy; Hillen­
brand et al. 1992), which results into an estimate of the
circumstellar mass in a region of 0.12 pc size of !0.2 M fi .
The molecular survey of Hillenbrand (1995) yields a mass
estimate of M cl =250 M fi in a region of ¸1.0 pc size. High
resolution observations by Fuente et al. (1998) show that
on a scale of 0.08 pc the amount of gas and dust is reduced
to ¸3.5 M fi .
(Fig. 47). Our K­band image show a low source sur­
face density field, without a central enhancement. This

18 L. Testi et al.: A search for clustering around Herbig Ae/Be stars. II
Fig. 40. MWC 758. Top left: J­band image; top right: K­band image; bottom left: colour­colour diagram; bottom right:
K­band source surface density profile.
Fig. 41. RR Tau. Top left: J­band image; top right: K­band image; bottom left: colour­colour diagram; bottom right: K­band
source surface density profile.
Fig. 42. HK Ori. Top left: J­band image; top right: K­band image; bottom left: colour­colour diagram; bottom right: K­band
source surface density profile.
result is consistent with what has been found by Hillen­
brand (1995) in her search for young groups around Herbig
AeBe stars.
5.45. Z CMa (BD\Gamma11 ffi 1760; HD 53179; MWC 165)
The distance (1150 pc) is from Hillenbrand et al. (1992)
and spectral type F5. The spectral type classification is
very uncertain and the values quoted in the literature span
the range A0­F5. It is not wise to determine luminosity
and age from the V­magnitude and the (B­V) colour.
(Fig. 48). In our images the bright star is surrounded
by a strong diffuse emission. No density peak is detected
around the star. The photometry is affected by the sys­
tematic uncertainties described in Paper I and an offset
in the H band magnitudes is evident in the colour­colour
diagram.
6. Summary
With the aim of searching for young star clusters around
intermediate mass stars, we have selected a sample of 45
Herbig AeBe stars, 43 of which cover almost uniformly
the spectral range from O9 to A7. From data existing in
the literature we have selected a set of stellar parame­
ters (spectral type, distance from the Sun, V­magnitude
and B--V colour), from which we have calculated effective
temperature and bolometric luminosity for each star. Us­
ing the theoretical PMS evolutionary tracks of Palla &
Stahler (1993), we have evaluated the age of almost all
the stars with spectral type later than B5.
The field around each star has been imaged in the near­
infrared with a moderately large field of view and sensitiv­
ity. In 22 fields we found a group of stars likely associated
with the Herbig AeBe star and determined the two rich­
ness indicators NK and I C , as well as the radius of the
group. The typical size of the detected groups is ¸ 0:2 pc.
This value is in agreement with that found by other au­
thors in various young stellar clusters (Hillenbrand 1995;
Carpenter et al. 1997). It is remarkable that stellar groups
with a few to several hundred members share similar sizes,
which in turn correspond to the typical sizes of dense cores
in molecular clouds.
The observations presented in this paper constitute
the dataset for our study of the clustering around Her­
big AeBe stars (Paper I; Testi et al. 1998).
Acknowledgements. We thank the TIRGO and ARNICA staff,
especially Filippo Mannucci, for nice scheduling and service
observing. LT would like to thank the NOT staff for help
and hospitality. Special thanks are due to Colin Aspin, Leslie
Hunt, Amanda Kaas and Ruggero Stanga who made the NOT
run a very pleasent and fruitfull one. The NOT observing
run has been partially supported by the Dipartimento di As­
tronomia e Scienza dello Spazio of the Universit`a di Firenze.
This work was partly supported by ASI grant ARS­96­66 and
CNR grant 97.00018.CT02 to the Osservatorio di Arcetri. Sup­
port from C.N.R.--N.A.T.O. Advanced Fellowship program and
from NASA's Origins of Solar Systems program (through grant
NAGW--4030) is gratefully aknowledged. This search has made
use of the Simbad database, operated at CDS, Strasbourg,
France.
A. Derivation of absolute magnitudes and colour
indexes from theoretical evolutionary tracks
In this Appendix we will briefly describe the method that
we have used to transform the K­completeness absolute
magnitude given in Table 1 into an estimate of the low­
est mass detectable in each field, the so­called minimum
mass. The discussion follows closely the method described
in Meyer (1996).
Firstly, we need to convert the PMS evolutionary
tracks of D'Antona & Mazzitelli (1994) from the theoret­
ical HR diagram Log L ? , Log T eff into the observable
one MK , (V--K), where MK is the absolute K magnitude.
We have used the calibrations of Schmidt­Kaler (1981),
Bessel (1979; 1991), Bessel & Bret (1988) and Koorn­
neef (1983) for dwarf stars to compile tables of the bolo­
metric corrections at V band (BCV ) and the (V--K) colour
index as a function of the effective temperature (T eff ).
These relations are shown in Fig. 49. For each value of L ?
and T eff , we can then compute MK as:

L. Testi et al.: A search for clustering around Herbig Ae/Be stars. II 19
Fig. 43. MaC H12. Left: K­band image; right: K­band source surface density profile.
Fig. 44. LkHff 198. Top left: J­band image; top right: K­band image; bottom left: colour­colour diagram; bottom right: K­band
source surface density profile.
Fig. 45. Elias 1. Top left: J­band image; top right: K­band image; bottom left: colour­colour diagram; bottom right: K­band
source surface density profile.
MK = 4:725 \Gamma 2:5 Log(L ? =L fi ) \Gamma BCV(T eff ) \Gamma (V \Gamma K)(T eff )
where 4.725 is the assumed absolute V magnitude of the
Sun. The colour­magnitude (V--K, MK ) diagram result­
ing from the transformation of the D'Antona & Mazz­
itelli (1994) ``CM Alexander'' (their fig. 3) tracks is shown
in Fig. 50.
We can now derive for each stellar mass the run of the
K absolute magnitude with time. This is shown in the up­
per panel of Fig. 51 for masses in the interval 2.5--0.1 M fi .
The peak in MK that appears for the more massive stars
at Log(age)¸ 6:2--7.4 is due to the transition from the con­
vective to the radiative section of the evolutionary tracks
(cfr. Fig. 50 and Fig. 3 of D'Antona & Mazzitelli 1994).
We can see that in the range of ages (t! 10 Myr) and
minimum masses considered in this paper (see Tables 1
and 2), the MK of a star of a given mass is a monoton­
ically increasing function of time. For this reason, given
a K absolute completness magnitude, the minimum mass
detectable is a function of time: as the age of the cluster
increases we loose sensitivity on the lowest mass members.
In graphical form this is presented in the lower panel of
Fig. 51, where the masses corresponding to MK are plot­
ted for isochrones between 0.1 to 10 Myr.
We have used this last figure to derive the minimum
mass in each field from the de­reddened K limiting mag­
nitude M c
K ­AK and the age of the Herbig AeBe star for
two values of AK=0 and 2 mag.
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L. Testi et al.: A search for clustering around Herbig Ae/Be stars. II 21
Fig. 49. Adopted BCV vs. T eff and (V--K) vs. T eff relations,
top and bottom panel respectively. Filled triangles are from
the M­dwarfs calibration of Bessel (1991), filled circles are a
compilation from the various references given in the text, the
dotted line is the linear interpolation that we have used.
Fig. 50. Colour-- magnitude diagram with the D'Antona &
Mazzitelli (1994) tracks. The dotted lines show the evolution­
ary tracks for 0.1, 0.15, 0.2, 0.3, 0.4, 0.5, 0.7, 1.0, 1.2, 1.5, 2.0,
and 2.5 M fi , respectively. Continuous lines show the isochrones
at 0.1, 1, 10, and 100 Myr.

22 L. Testi et al.: A search for clustering around Herbig Ae/Be stars. II
Fig. 51. Top panel: absolute K magnitude as a function of
time for M?/M fi = 2:5, 2.0, 1.5, 1.2, 0.9, 0.7, 0.5, 0.3, 0.2, 0.1,
respectively (from bottom to top); bottom panel: M? versus
MK for isochrones in the interval 0.1--10 Myr. Given the K
absolute magnitude and the age of a star it is possible to derive
the corresponding mass, using the appropriate isochrone.