Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.apo.nmsu.edu/35m_operations/35m_manual/Instruments/Grim/PDF/GrimII_Users_manual.pdf Дата изменения: Thu Jul 22 23:41:08 2004 Дата индексирования: Sun Apr 10 09:26:54 2016 Кодировка: Поисковые слова: south pole

GRIM II User's Manual
Alan Watson, Mark Hereld, and Bernie Rauscher 15 March 1997


`Jeeves,' I said, `haveyou ever pondered on Life?' `From time to time, sir, in my leisure moments.' `Grim, isn't it, what?' `Grim, sir?' `I mean to say, the di erence between things as they look and things as they are.' |P.G. Wodehouse anticipating the advantages of infrared astronomy in Very Good, Jeeves!

i


Contents
1 Introduction 2 Optics 3 Detector
3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 1.1 GRIM II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 User's Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3 Mailing List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1

1 1 2

Detector Characteristics . . . Detector Operation . . . . . . Bias and Dark Current . . . . Response Uniformity . . . . . Non-Linearity and Saturation Bad Pixels . . . . . . . . . . . Residual Image . . . . . . . . Peculiarities . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . .

.5 .5 .6 .6 .6 . 12 . 12 . 14 . . . . . . . . . . . . . .

3 5

4 Operation

4.1 REMARK . . . . . . . . 4.2 MC . . . . . . . . . . . . 4.2.1 Commands . . . 4.2.2 Procedures . . . 4.2.3 Example Session 4.3 Hangs . . . . . . . . . .

15

15 15 16 20 23 24

5 Imaging

5.1 Cameras . . . . . . . . . . . . . . . . 5.2 Neutral Density Filters . . . . . . . . 5.3 Filters . . . . . . . . . . . . . . . . . 5.3.1 Transmittances . . . . . . . . 5.3.2 Zero Points and Backgrounds 5.3.3 Broad Band Filters . . . . . . 5.3.4 Narrow Band Filters . . . . . 5.4 Bright Limits . . . . . . . . . . . . . ii

25

25 25 25 25 28 28 35 35


5.5 Flat Field Images . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 5.6 Basic Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

6 Spectroscopy
6.1 6.2 6.3 6.4

Capabilities Flat Fields Wavelength Absorption

...... ...... Calibration Standards

... ... .. ...

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

39
39 39 39 41

7 Extinction 8 Standards

8.1 Photometric Standards . . . . . . . . . . . . . . . . . 8.1.1 Elias et al. JH K ,CO, and H2 O Standards . 8.1.2 Carter & Meadows JH K Standards . . . . . 8.1.3 Casali & Hawarden JH K Standards . . . . . 8.1.4 Wainscoat & Cowie K Standards . . . . . . 8.1.5 Manufactured K Standards . . . . . . . . . . 8.1.6 Absolute Calibration . . . . . . . . . . . . . . 8.2 Spectrophotometric Standards . . . . . . . . . . . . 8.2.1 Bohlin Spectrophotometric Standards . . . . 8.2.2 Manufactured Spectrophotometric Standards 8.3 Stellar Colours . . . . . . . . . . . . . . . . . . . . . 8.4 Stellar Spectra . . . . . . . . . . . . . . . . . . . . .
0 0

. . . . . . . . . . . .

. . . . . . . . . . . .

. . . . . . . . . . . .

. . . . . . . . . . . .

. . . . . . . . . . . .

. . . . . . . . . . . .

. . . . . . . . . . . .

42 44

44 44 45 45 45 45 45 46 46 46 46 46

9 Headers

48

iii


List of Figures
2.1 Optical Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1 3.2 3.3 3.4 3.5 3.6 Bias Image (IRAF format 1 second) Bias Image (FITS format 1 second) Flat Field Image in K . . . . . . . . Ratio of Flat Fields Images in J and Non-linearity and Saturation . . . . Bad Pixels . . . . . . . . . . . . . . .
obj4 fexp

4

.... .... .... K .. .... ....

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

.7 .8 .9 . 10 . 12 . 13

4.1 The 4.2 The 5.1 5.2 5.3 5.4 5.5 5.6 5.7

procedure . . . . . . . . . . . . . . . . . . . . . . . . . 22 procedure (for n =5) . . . . . . . . . . . . . . . . . . . 23 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 27 30 31 32 33 34

Camera Orientations for Imaging . . . . . . . . . . . Neutral Density Filter Transmittances . . . . . . . . Filter Transmittances . . . . . . . . . . . . . . . . . Filter Transmittances (continued) . . . . . . . . . . . Filter Transmittances (continued) . . . . . . . . . . . Filter Transmittances (continued) . . . . . . . . . . . Broad Band Filter and Atmospheric Transmittances

7.1 Model Atmospheric Transmitances . . . . . . . . . . . . . . . . . 43

iv


List of Tables
4.1 Modes Values and Names . . . . . . . . . . . . . . . . . . . . . . 17 4.2 Scale Values and Names . . . . . . . . . . . . . . . . . . . . . . . 17 4.3 Filter Values and Names . . . . . . . . . . . . . . . . . . . . . . . 18 5.1 5.2 5.3 5.4 Camera Con gurations for Imaging Filter Characteristics . . . . . . . . Filter Zeropoints and Backgrounds Imaging Dome Flat Characteristics . . . a .... .... .... t f=5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 29 29 36

6.1 Wavelength Coverage in m . . . . . . . . . . . . . . . . . . . . . 40 9.1 Header Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

v


Chapter 1

Introduction
1.1 GRIM II
GRIM II is the near infrared camera and low resolution spectrograph in service on the Apache Point Observatory 3.5 meter telescope. GRIM II has a 256 256 NICMOS-3 detector and works between 1.0 m and 2.5 m. In imaging mode it has three pixel scales of about 0.48, 0.24, and 0.11 arcsec/pixel and a large number of broad and narrow band lters. In spectroscopic mode it has three resolutions of about 200, 400, and 800. GRIM II was designed and built byMark Hereld, Bernie Rauscher, Scott Severson, and Bob Loewenstein of the Univeristy of Chicago with engineering support from Dale Sandford, Fred Mrozek, Dave Fischer, and Je Sundwall.
How should GRIM II and APO be acknowledged in publications?

1.2 User's Manual
This manual has two purposes: to provide a basic introduction to near infrared imaging and low-resolution spectroscopy for astronomers familiar with optical CCD imaging and spectroscopy and to describe the speci cs of performing such observations with GRIM II. The authors of this manual are Alan Watson alan@oldp.nmsu.edu Mark Hereld hereld@bucephalus.uchicago.edu Bernie Rauscher B.J.Rauscher@durham.ac.uk Direct and indirect contributions have also been made by Eddie Bergeron Jon Brinkmann Nancy Chanover Karen Gloria Jon Holtzman Mike Ledlow 1


Bob Loewenstein Dan Long James Rhoads Scott Severson This manualis anevolving document the lastest version is available as
ftp://oldp.nmsu.edu/pub/alan/grim/man.ps.Z

Versions are identi ed by the date on the cover. If you nd errors or have suggestions for improvements, please send them to the authors.

1.3 Mailing List
Another source of information on GRIM II is the GRIM II mailing list maintained byMichael Strauss. An archive of mail sent to the list and instructions for subscribing to and sending mail to the list are available from
http://www.astro.princeton.edu/APO/apo35-grim/INDEX.html

2


Chapter 2

Optics
The optical layout of GRIM II is shown in Figure 2.1. All of the optical components are contained in a cryogenic dewar (which is purple and very pretty). The f=10 beam from the telescope enters the dewar and comes to a focus at the slit wheel. After that it passes through the eld lens, collimator lens, grism wheel, two lter wheels, and then the lenses and fold mirrors of one of the three cameras mounted on the camera carousel, before coming to a focus on the detector. The grism wheel contains an aperture stop, the grism, and 3%, 13%, and 25% transmission neutral density lters. The aperture stop is a circular aperture without a central obscuration to block the high-emissivity central hole in the primary or rotating vanes to block the spiders. The lter wheels contain a large number of broad and narrow band lters along with a solid plate known as the `blank-o ' or `dark' lter. The f=5 camera has only one fold mirror but the f=10 and f=20 cameras havetwo. Thus, the image formed bythe f=5 camera is ipped about one axis compared to the images formed by the other two (see x5.1). The throughputs of the cameras is slightly di erent as they eachhave di erent optics. The oblique re ections within GRIM II and from the tertiary mirror induce polarization. Since GRIM II and the tertiary rotate with repect to each other under normal circumstances, there is a photometric modulation of even unpolarized sources. The amplitude of this modulation is though to be in the vicinityof 1% RMS. Polarized sources will also su er from modulations and o sets because of instrumental polarization.

3


Accessory Ring

Slit Wheel

Field Lens

Collimator Lens

Detector

Camera Carousel

Grism and Filter Wheels

Figure 2.1: Optical Layout

4


Chapter 3

Detector
3.1 Detector Characteristics
GRIM II has a 256 256 NICMOS-3 detector. The detector is sensitive from 0.8 m to 2.5 m. The long wavelength cuto lies at the red end of the atmospheric K window and is su ciently short that low backgrounds can be obtained by cooling the detector and optics to 77 K with liquid nitrogen. The device is split into quadrants eachof which has its own ampli er. The quadrants are read simultaneously. The detector has a gain of about 4.7 electrons/DN and an e ective read noise of about 110 electrons. Thus, the read noise is larger than the Poisson noise for exposures of less than about 2500 DN.

3.2 Detector Operation
GRIM II does not have a shutter. Instead, exposures are controlled electronically. GRIM II operates in a `reset, read, read' or `double correlated sampling' mode this mode has lower noise than the `reset, read' mode, whichisanalogous to themodeinwhich CCDs are operated. An exposure begins with a reset, which sets the bias in each pixel. A short time after being reset, the chipisread. The read is non-destructive and merely samples the voltage in each pixel. After a further time the chip is read once more. The GRIM II controller does not allowmultiple rst and second reads. The signal n is the di erence between the rst and second reads. The time between the reset and the rst read is about 0.95 seconds. The time between the two reads is the exposure time t and is t =0:901 + OPENTIME (3.1) in seconds where OPENTIME is a header value. The exposure time is about 0.2 seconds less than the time requested using REMARK or MC. The shortest exposure time possible is 1.0 seconds (corresponding a requested time of 1.2 seconds). 5


3.3 Bias and Dark Current
Between the rst and the second reads, the signal chain bias level changes. Thus, even a short dark exposure has values which are far from zero. To obtain the true signal, one must subtract a bias image. The amountbywhich the bias level changes depends on the exposure time in the sense that longer exposures have more negative bias levels. For this reason, one must construct a separate bias image for each exposure time used. Since bias images can only be constructed from dark exposures, subtracting a bias image also removes the dark current. As the dark current is small, this has a negligible e ect on subsequent corrections for non-linearity. Dark images can be taken using the `dark' or `blank o ' lter. IRAF images obtained with GRIM II have a constant of 10000 DN added to them by the MC. This allows the values to be comfortably represented as 16-bit unsigned integer. FITS images obtained with GRIM II do not have this constant added because BZERO header value can be used to achieve the same ends. The values in short dark exposures are about ;2000 DN for FITS images and 8000 DN for IRAF images. 1 second bias images are shown in Figure 3.1 for IRAF images and Figure 3.2 for FITS images. The bias uctuates, giving rise to the bands seen in the lower rows of each quadrant. The amplitude of the uctuation seems to depend primarily on the exposure, so that the bands largely disappear when two similar exposures are subtracted but remain when two di erent exposures are subtracted. In consequence, the bands largely disappear in the course of the normal processing of ob ject frames (as sky frames are subtracted). Unfortunately they remain in ats (as a low exposures are subtracted from a high exposures) at the few percent level. One approach to this problem which seems to work well is normalizing each row individually so that the central columns of the at have the same mean. Low-level diagonal banding in the lower right quadrant has also been reported.

3.4 Response Uniformity
The response of the detector in GRIM II is fairly uniform compared to many NICMOS-3 detectors. Figure 3.3 shows a at eld image in K . However, the response changes as a function of wavelength Figure 3.4 shows the ratio of at eld images in J and K .

3.5 Non-Linearity and Saturation
Since the in uence of the ARC board does not extend to waiving the laws of physics, the GRIM II detector is by necessity slightly non-linear. The nonlinearity is about 6% over the working range of about 28000 DN and the corrections for non-linearity can be as large as 10%. Furthermore, those unaware 6


Figure 3.1: Bias Image (IRAF format 1 second)

7


Figure 3.2: Bias Image (FITS format 1 second)

8


Figure 3.3: Flat Field Image in K

9


Figure 3.4: Ratio of Flat Fields Images in J and K

10


of the mode in which GRIM II operates can inadvertently expose the chip beyond its working range saturation can occur for signals as low as 13000 DN. Fortunately, the non-linearitycan be characterized and corrected and with forewarning it is not di cult to stay within the working range. The origin of the non-linearity suggests that its characteristics should be stable with time. The non-linearity in a near infrared array occurs because each pixel in the array is e ectively a capacitor. The pixel is read by sensing the voltage across the capacitor. At the start of the exposure, the capacitor is biased. Thereafter, it accumulates charge and the bias decreases. If the capacitance of the pixel were constant, the voltage would be linearly related to the accumulated charge. Unfortunately, the capacitance increases with decreasing bias and the relation between accumulated charge and voltage is sub-linear. Alan Watson and Nancy Chanover investigated and characterized the nonlinearity of GRIM II in June 1996. The full text of their report is available as
ftp://oldp.nmsu.edu/pub/alan/grim/lin.ps.Z

Their main conclusions are sumarized here. The non-linearity can be adequately modelled as a straight line, that is the signal N that would be accumulated by a truly linear detector can be related to the actual signal n by

n =(1 ; 1 N )N

(3.2)

where 1 is a constant. Inverting this expression to correct for the non-linearity is hampered bythe fact that the detector accumulates charge for a time t1 between the reset and the rst read and then a further time t between the rst read and the second read. As noted in x3.2, the actual exposure time is di erent both from the requested exposure time and the OPENTIME header value. The signal n is the di erence between the rst and second reads. (A bias image needs to be subtracted to obtain n.) The value of the signal N that would be given by a perfectly linear detector is

t +2 N = 1 ; (1 ; 42 1 (n(t +2t )t1 )= t) 1 1
1

1=2

t:

(3.3) (3.4) (3.5)

From eight sequences of increasing exposures, they found =2:18 10
;

6

and

t1 =0:95:

Contours of the fractional correction are shown in Figure 3.5 the corrections can be as large as 10%. 11


30000 25000 20000 Signal n
1.10
1.09

1.10

1.09
1.08

1.07
1.06
1.05
1.04

1.08 1.07
1.06
1.05 1.04

15000 10000 5000 0 0 1 2

1.03

1.03

1.02
1.01

1.02
1.01

3

4 5 6 Exposure Time t

7

8

9

10

Figure 3.5: Non-linearity and Saturation The full well of the detector is only about 28000 DN. Since charge accumulates between the reset and the rst read, saturation can occur well before the signal approaches this value. Toavoid saturation, the signal must be kept below the values indicated by the thick line in Figure 3.5. Thus, in a 1 second exposure the signal must be kept below about 13000 DN. (The `signal' in question here is the value in the image after subtracting the bias, which is about ;2000 for FITS images and about 8000 for IRAF images.)

3.6 Bad Pixels
The GRIM II detector is cosmetically excellent compared to many other similar detectors. Figure 3.6 shows an image of the bad pixels constructed by dividing a 15000 DN at eld from a 1500 DN at eld and agging pixels that deviated from the mean by more than 10%. Most of the bad pixels are isolated, although there are three clumps of bad pixels, one of which is fairly close to the center of the detector. The number of bad pixels is expected to increase slowly with time.

3.7 Residual Image
Like all NICMOS-3 detectors, the detector in GRIM II su ers from residual image. This has not been well characterized. The conventional wisdom is that taking a series of bias exposures helps to eliminate a residual image. 12
It might be useful to characterize this.


Figure 3.6: Bad Pixels

13


3.8 Peculiarities
Columns 128 and 256 are o (128 256), (256 128), and pixels (128 i) and (256 i) pixels (128 i + 1) and (256 set down by one row. The values in pixels (128 128), (256 256) in the image are garbage. The values in in the image actually correspond to the values in i + 1) on the detector.

14


Chapter 4

Operation
GRIM II can be controlled by normal users with either the REMARK interface or the MC interface. Both allow the telescope and instrument to be controlled over the Internet and both can automatically copy images to a remote host using FTP.

4.1 REMARK
REMARK runs on a networked Macintosh and provides a remote, graphical interface for controlling both the telescope and instruments. REMARK was written by Bob Loewenstein. The documentation for REMARK can be found on the APO home page (http://www.apo.nmsu.edu). At the time of writing, the documentation describing the operation of GRIM II using REMARK is incomplete.

4.2 MC
MC runs on tycho.apo.nmsu.edu and provides a command line interface for controlling both the telescope and instruments. MC was written by Brian Yanny. The documentation for MC can be found from the APO home page (http://www.apo.nmsu.edu). The advantage of the MC over REMARK is that it can be programmed procedures can be written to perform sequences of tasks such as exposures and o sets. An MC session can be started on tycho with
mcnode

An MC status display can be started on
mcnode -s

tycho

with It is also

in a 80 26 VT100-compatible window (e.g., useful to monitor the hub log on tycho with 15

xterm -geom 80x26).


tail -f /home/apotop/syslog/hub.log

In particular, FTP error messages appear in the hub log.

4.2.1 Commands

The most common MC commands are listed here. The descriptions are somewhat abbreviated and often do not show all of the options consult the MC documentation for more details on these commands and the less common commands.
priority

The priority command sets the priority of this MC session. A priority value of 0 allows only harmless commands a priority value of 1 allows all commands. A new MC session initially has a priorityof 0.

priority

grimmove

The grimmove command moves the slit wheel, grism wheel, lter wheels, and camera carousel in GRIM II. The numerical values of mode, scale, and filter are listed in Tables 4.1, 4.2, and 4.3. These values appear as the MODE, SCALE, and GFILTER header values. Occasionally, a move will fail and need to be repeated. The grimstatus command requests a message describing the status of the grim optical components. The numerical values returned correspond to the mode, scale, and lter values listed in Tables 4.1, 4.2, and 4.3.

mode scale f ilter

grimstatus

inst

The inst command sets the current instrument for the nexpose commands. An instrument value of grim speci es GRIM II. nexpose itime=itime n=n reduce='send>ftp'] The nexpose command takes n exposures eachof itime seconds. As noted in x3.2, the actual exposure time is about 0.2 seconds shorter than the value of itime. If reduce='send>ftp' is speci ed and an FTP connection has been established with the loginftp command, the image is FTP-ed to the remote host.
grimabort

instrument

The

slew

command aborts the current exposure. hh:mm:ss +j-]dd:mm:ss epoch=epoch The slew command executes a slew to the speci ed position. A slew can be aborted with the stop tcc command.
grimabort

16


Mode image grism image grism image image image

Value Name 0 image with slit 1 grism+slit with slit 2 image+slit without slit 3 grism with 3% ND lter 4 image+nd3 with 13% ND lter 5 image+nd13 with 25% ND lter 6 image+nd25 Table 4.1: Modes Values and Names

Scale Value Name f=5 1 f5 f=10 3 f10 f=20 5 f20 f=20 short 13 f20short f=20 long 21 f20long Table 4.2: Scale Values and Names

17


Filter open dark

J H K K Ks Kdar
0

1.08 1.09 1.24 1.28 1.58 1.64 1.70 1.99 2.12 2.17 2.21 2.25 2.26 2.30 2.34

k

m m m m m m m m m m m m m m m

Value Name 13 open 0 dark 1 j 2 h 3 k 4 kprime 5 ks 7 kdark 15 1.08 16 1.09 17 1.24 18 1.28 8 1.58 19 1.64 9 1.70 20 1.99 21 2.12 22 2.17 23 2.21 24 2.25 6 2.26 25 2.30 26 2.34

Table 4.3: Filter Values and Names

18


stop tcc

command aborts a slew. offset x y ty pe abs] The offset command executes an o set of x arcseconds in the x direction and y arcseconds in the y direction. If abs is speci ed, the o set is relative to the last slew, otherwise the o set is relative to the last o set of the given type. The type value can be inst or ob j to specify `instrument' or `ob ject' o sets. Instrument and ob ject o sets are independent. Ob ject o sets have a coordinate system that always has x west and y north. Ob ject o sets are re ected in the RA, DEC, RAOFF and DECOFF header values. Instrument o sets have a coordinate system which rotates with the instrument. At 0 degrees rotation, x is east and y is south. With the f=5 camera, the x and y axes of the coordinate system match the axes of the detector, but with the other cameras the coordinate system is ipped about the x axis. Instrument o sets are re ected in the the X and Y header values.
stop tcc rotate

The

command sets the rotator position angle to angle. object or horizon. The rotation is recorded ROTATION header values. An ob ject rotation of 0 degrees gives the tations shown in Table 5.1 and Figure 5.1. A horizon rotation of 0 d places the slit parallel with the horizon. The

angle type
rotate

type values can be

The in the orienegrees

focus

The focus command sets the telescope focus to f ocus. When an instrument is mounted, the operator normally sets the focus to something reasonable. The imdir command speci es the directory in which images are to be created. The directory must have write permission for all users. Images are created in /export/images by default.

f ocus

imdir

dir

pref ix places places filetype ty pe seq number
diskname

The diskname, places, filetype, and and type of image created. 19

seq

commands specify the name


The le name is pref ix, followed by the sequence number padded with _ zeros to a width of places,followed byeither .hhh or hhd if IRAF images are being written or .fit if FITS images are being written. The filetype command speci es that IRAF or FITS images are created depending on whether type is iraf or fits. The seq command sets the sequence number for the next exposure.
subscribe

The subscribe command determines which messages are printed in this MC session. Values for type are message, monitor, and status. Values of level are 0, 1,and 2,with 0 switching messages o . The MC is quite verbose. It is useful to have two MC session running simultaneously, with one being used only for commands and having all messages turned o and the other being used only for messages. The loginftp command establishes an FTP connection to the directory dir on host host. You will be prompted for a password.

type level

loginftp

hostname username

senddir=

dir

4.2.2 Procedures

MC procedures can be written in the TCL language. Information on TCL is available from http://www.NeoSoft.com/tcl/. Writing MC procedures is not trivial. The basic model is described by Brian Yanny in the MC documentation. A somewhat higher-level model has been suggested byAlan Watson in a message to the GRIM II mailing list on 8 July 1996. Anumber of useful procedures, which can also serve as examples from which to create your own, are available from
ftp://oldp.nmsu.edu/pub/alan/grim/mc.tcl

This le also exists on

tycho.apo.nmsu.edu

as
tycho.apo.nmsu.edu

~visitor1/alan/grim/mc.tcl mcnode

To use these procedures, start an MC session on command and then type:

with the

source ~visitor1/alan/grim/mc.tcl start config loginftp senddir=

hostname username

dir

Because of the way MC works, many of these procedures return before they have completed do not attempt to execute another command until the message stating that the procedure has completed. These procedures will attempt to FTP any exposures they take. The available procedures are: 20


start

This command must be issued before any others. This command should be issued to relinquish control of GRIM II. Query grim for the current mode, camera con guration, and lter and print them in recognizable forms. This command must be issued after the initial start command but before any others. Set the mode according to mode,which can be one of one of names listed in Table 4.1. Occasionally,a move will fail and need to be repeated. Set the scale according to scale, which can be one of names listed in Table 4.2. Occasionally,a move will fail and need to be repeated. Set the lter according to f ilter, which can be one of names listed in Table 4.3. Occasionally,a move will fail and need to be repeated.

end

config

mode

mode

scale

scale

filter

filter

Move the telescope arcsec north, south, east, and west. center xy Move an ob ject that is at pixel location (x y)tothe center of the detector.
exp

arcsec south arcsec east arcsec west arcsec
north

exptime n Take n exposures each of duration exptime. (The procedure actually requests an exposure of 0.2 seconds longer than exptime so that the actual exposure corresponds to the exptime. See x3.2.) obj1 exptime n sk y x skyy Take 2 sequences of n exposures each of duration exptime. The sequences
are ob ject then sky. The ob ject exposures are taken at the current position. The sky exposures are taken at an instrument o set of skyx and skyy arcsec. The telescope is left at the initial position. 21


d 4 1

d

5 skyy 3 0 2 skyx

8

d

6 d

7

Figure 4.1: The
obj4

obj4

procedure

exptime n skyx skyy d Take 8 sequences of n exposures each of duration exptime. The sequences

are sky, ob ject, ob ject, sky, sky, ob ject, ob ject, sky. The ob ject exposures are each centered at the corner of a square of side d arcsec centered on the current position. The sky exposures are each centered at the corner of a square of side d arcsec centered on an instrument o set of skyx and skyy. The telescope is left at the initial position. This is illustrated in Figure 4.1. The telescope starts at position 0, and then takes a sequence of exposures at positions 1, 2, 3, 4, 5, 6, 7, and 8, before nally returning to position 0 again.
home

Return the telescope to its position after the last slew command or the last center, north, south, east, or west procedure. This is useful if an obj1 or obj4 procedure has to be aborted.

fexp

exptime f start f end n Take a focus run of n exposures each of duration exptime with the focus set to values equally spaced between fstart and f end inclusive. The
focus star should be roughly centered before this procedure is run. The 22


1 2 3 0 4

focus = fstart

5

focus = fend
fexp

Figure 4.2: The

procedure (for n =5)

exposures are o set in the north{south direction with a larger gap before the nal image. This is illustrated in Figure 4.2 for n =5. The telescope starts at position 0, and then takes a sequence of exposures at positions 1, 2, 3, 4, and 5, before nally returning to position 0 again. The exposures can be combined to form a single focus image by subtracting the median from the mean. The operator can advise you of a reasonable value for the focus. In this example session, command are set in type. Load procedures and initialize:

4.2.3 Example Session

this type

and comments in normal

source ~visitor1/alan/grim/mc.tcl start config

Tell the MC to create FITS les like
filetype fits diskname 970120. places 4 seq 1 mode image scale f5 filter h

970120.0001.fit:

Set f=5 imaging mode with the H lter:

23


Slew to an ob ject:
exp 1 1

slew 00:01:02 -03:04:05 epoch=2000

Take a nder exposure:
north 10 east 5

Move the telescope 10 arcsec north and 5 arcsec east: Take 3 exposures each of 5 seconds, o set 600 arcsec to sky,take 3 more, and return to the ob ject:
obj1 5 3 600 0

4.3 Hangs
Sometimes GRIM II hangs just after starting an exposure. If you are using REMARK, you can recover by closing and reopening the exposure control window. If you are using MC, you can recover by issuing a grimabort command.

24


Chapter 5

Imaging
5.1 Cameras
GRIM II has three cameras: f=5, f=10, and f=20. Table 5.1 lists the pixel scales, elds of view, and orientations at 0 degrees rotation of the cameras. The orientations assume that the origin is at the lower left. The plate scales were measured by Alan Watson and reported to the GRIM II mailing list on 29 January 1997. The uncertainties in the pixel scales are estimated to be about 0.001 arcsec. Figure 5.1 shows the orientation of the cameras. If you are working in f=10 or f=20 and switchto f=5 to acquire an ob ject, remember that the orientation will change.

5.2 Neutral Density Filters
There are three neutral density lters known as ND03, ND13, and ND25. Unfortunately, these lters are visible light neutral density lters in the infrared they are not especially neutral and have similar transmissions. Their transmissions are shown in Figure 5.2. The ND13 lter supplies the most blocking in the infrared and has transmissions of about 10% in J , 25% in H , and 35% in K.

5.3 Filters

Table 5.2 lists for each lter the central wavelength 0 T d = Td , width R Td = max(T ), resolution R = 0 , and integrated transmittance R Td . Transmittance curves are not available for a number of lters the values for these lters are estimates. Figures 5.3 to 5.6 show the transmittances of the lters. The transmittances are available in electronic form as 25

5.3.1 Transmittances

R

R


Camera Pixel Scale Field of View N E arcsec arcsec f=5 0.473 120 down right f=10 0.236 60 up right f=20 0.113 30 up right Table 5.1: Camera Con gurations for Imaging

(a) f/5

(b) f/10 and f/20 N E E N

Figure 5.1: Camera Orientations for Imaging

26


Figure 5.2: Neutral Density Filter Transmittances

27


ftp://oldp.nmsu.edu/pub/alan/grim/filters.tar.Z

No signi cant shifts in focus between the lters are expected and none have been reported.

5.3.2 Zero Points and Backgrounds

Typical zero points and backgrounds at one airmass for the broadband lters are listed in Table 5.3. These zero-points can be used to estimated e ciencies, but should not be used for calibration. The zero points are de ned by

The backgrounds will vary with the airmass, season, atmospheric conditions, and mirror re ectivity. These measurments were made on a photometric nightin January 1997, just after the mirrors were realuminized, with an air temperature of about 275 K. The throughputs of the narrow band lters can be estimated from the throughputs of the broad band lters by scaling by the ratios of the integrated transmissions from Table 5.2. The background in the near infrared is dominated by many OH lines in the J , H , and the blue end of the K window and thermal emission at the long end of the K window. This complex structure makes it more di cult to estimate narrowband backgrounds from the broad band measurements. The transmittances of the GRIM II broad band lters are shown in Figure 5.7. Also shown is a representative MODTRAN-3 model atmospheric transmittance curve. The JH K lters are shown with solid lines, the K lter with a dotted line, the Ks lter with a dashed line, and the Kdark lter with a dashed-dotted line. The K lter was designed for deep imaging from Mauna Kea and has been described by Wainscoat & Cowie (1992). It has a shorter e ective wavelength than the K lter and so has a lower thermal background. However, its blue cut o encroaches on the atmospheric H2 Obandbetween the H and K windows on Mauna Kea this is not so much of a problem, but at lower sites the absorption reduces the throughput of the lter, makes the extinction correction more nonlinear, and introduces signi cant variablitity into the band pass of the lter. For these reasons, the Ks lter is probably a better choice for observations from APO. The Ks lter was designed for deep imaging from moderate altitude observatories. It will be used in the 2 Micron All Sky Survey. It has a longer blue cut o than the K lter but a shorter red cut o than the K lter. The Kdark lter is designed for low-background imaging from the South Pole (Nguyen et al. 1996 Ashley et al. 1996).
0 0 0

m ;2:5 log n + ZP _ where m is the standard magnitude and n is the signal in DN s 1 . _
;

(5.1)

Measurements would be useful.

5.3.3 Broad Band Filters

Does anyone have a reference for Ks ?

28


Filter

J H K K K K

0

1.08 1.09 1.24 1.28 1.58 1.65 1.70 1.99 2.12 2.17 2.21 2.25 2.26 2.30 2.34
1 2

s dark

m m1 m m m1 m m1 m1 m m2 m m m m m

m 1.265 1.646 2.187 2.114 2.155 2.359 1.084 1.094 1.235 1.282 1.580 1.647 1.700 1.990 2.120 2.161 2.210 2.248 2.260 2.297 2.342

0

m 0.267 0.339 0.399 0.343 0.324 0.147 0.013 0.010 0.011 0.015 0.010 0.019 0.050 0.020 0.030 0.032 0.100 0.025 0.055 0.028 0.091

=

0

R

0.211 0.206 0.182 0.162 0.150 0.062 0.012 0.010 0.009 0.012 0.006 0.012 0.030 0.010 0.014 0.015 0.045 0.011 0.024 0.012 0.039

m 0.221 0.276 0.305 0.310 0.300 0.113 0.007 He I P 0.006 OII 0.011 P continuum 0.016 FeII] CH4 H2 O 0.018 H2 v=1{0 S(1) 0.022 Br 0.062 CO o 0.020 continuum 0.047 H2 v=2{1 S(1) 0.022 CO 2{O band head 0.057 CO on

Td

No transmittance curve values are estimates. 1987 transmittance curve(see x5.3.4). Table 5.2: Filter Characteristics

Filter

J H K K

s

ZP Background mag DN s 1 arcsec 23.3 1100 23.1 5100 22.2 6300 22.4 4700
;

;

2

Table 5.3: Filter Zeropoints and Backgrounds

29


Figure 5.3: Filter Transmittances

30


Figure 5.4: Filter Transmittances (continued)

31


Figure 5.5: Filter Transmittances (continued)

32


Figure 5.6: Filter Transmittances (continued)

33


Figure 5.7: Broad Band Filter and Atmospheric Transmittances

34


Whether K , Ks , or Kdark give better signal-to-noise than K depends on colour of the ob ject and the background. Wainscoat & Cowie (1992) perform this calculation for their K lter on Mauna Kea, but their results may not be valid for APO. Since the K , K , Ks , and Kdark lters have di erent e ective wavelengths and band passes, the K , K , Ks , and Kdark magnitudes of an ob ject are all di erent in general.
0 0 0 0

GRIM II has a very wide selection of narrow band line lters, but is somewhat lacking in narrow band continuum lters. For some observations, broad band lters are adequate for the continuum. However, when imaging a weak line against a continuum or in the presense of other lines, this approach can fail. Some users have had success using nearby narrow band line lters (e.g., OII] with Pa and H2 v=1 ; 0 S(1) with Br ), but obviously one needs to be certain that the emission line in the `continuum' lter is su ciently weak. In earlier documentation, twocurves for 2.17 m lters are given. The 1987 curve has a peak transmission of 0.69 and a FWHM of 0.0286 m the 1992 curve has a peak transmission of 0.80 and a FWHM of 0.0224 m. On the strength of spectra taken through various lters with GRIM II, it is believed that the lter in GRIM II corresponds to the 1987 curve.

5.3.4 Narrow Band Filters

As discussed in x3.5, the detector saturates if it is exposed above a certain level. In the minimum exposure of 1 second, this occurs at a signal of 13000 DN above the bias. This sets a bright limit for the instrument. With the f=5 camera and 1 arcsec seeing, at most about 20% of the light from a point source lands in a single pixel. Using the zero points and backgrounds from x5.3.2, the bright limits for the minimum exposure of 1 second are J 11:3, H 11:1, K 10:4, and Ks 10:4. These limits will be 1.5 and 3.0 mag brighter for the f=10 and f=20 cameras and will change with seeing roughly as 5 log FWHM=arcsec. The ND13 neutral density lter can be used to allow observations of ob jects up to about 2.5 mag brighter at J , 1.5 mag brighter at H , and 1.0 mag brighter at K . (Note the the nuetral density lters are not neutral see x5.2.)

5.4 Bright Limits

5.5 Flat Field Images
Flat eld images can be contructed either from sky exposures or lamps on/o dome exposures. Whichever you elect, it is worth combining a number of exposures to minimize systematic errors and aiming to get a formal signal-to-noise ratio well in excess of 100. The advantage of sky ats is that the sky is in the far eld of the telescope the disadvantages are that the sky is not a continuum source, has a very di erent 35


Filter

Lamp faint quartz faint quartz faint quartz faint quartz faint quartz faint quartz bright quartz bright quartz bright quartz bright quartz bright quartz bright quartz bright quartz bright quartz bright quartz bright quartz bright quartz bright quartz bright quartz bright quartz bright quartz

J H K K K K

0

1.08 1.09 1.24 1.28 1.58 1.64 1.70 1.99 2.12 2.17 2.21 2.25 2.26 2.30 2.34

s dark

m m m m m m m m m m m m m m m

On O T S=N DN/s DN/s s 2750 0 3.6 175 2850 0 3.5 175 5300 3700 1.9 45 3750 1800 2.7 80 3750 2100 2.7 65 3250 2900 3.1 15 750 0 13.3 175 800 0 12.5 175 700 0 14.3 175 1300 0 7.7 175 1150 50 8.7 165 1200 0 8.3 175 5650 1200 1.8 130 2250 50 4.4 170 1000 50 10.0 165 1050 100 9.5 155 3050 550 3.3 135 950 250 10.5 120 2350 650 4.3 120 1050 400 9.5 95 2950 1300 3.4 85

Table 5.4: Imaging Dome Flat Characteristics at f=5

36


color from most astronomical ob jects, and scattered light and thermal emission from the telescope and instrument are not removed well. The advantages of lights on/o dome ats are that the source is a continuum, has a color somewhat appropriate to many astronomical ob jects (being a roughly 2000K black body), and scattered light and thermal emission from the telescope and instrument are removed well the disadvantages are that the source is in the near eld of the telescope and, at APO, dome ats must be taken o the mirror covers, whichmay cause additional problems. At the time of writing, the mirror covers and lamps can only be controlled by the telescope operator at APO. Table 5.4 gives some useful information for taking dome ats. The numbers are for the f=5 camera but can be trivially scaled to the f=10 and f=20 cameras. Table 5.4 lists for each lter the appropriate lamps (either the bright or faint quartz lamps), the rates with lamps on and o , the time to get about 10000 DN with the lamps on, and the formal signal-to-noise ratio S=N in a at constructed from a single on/o pair. The backgrounds in the K window will be very sensitive the the temperature of the telescope these data were taken with the telescopeat about4C.

5.6 Basic Techniques
Infrared imaging is normally performed by imaging the ob ject eld and one or more sky elds at slightly di erent pointings. The di erent pointing mitigate the presense of at eld errors and bad pixels and allow ob jects in the sky eld to be rejected when the sky exposures are combined. Sky exposures are required because it is impossible to at eld with su cient accuracy to detect ob jects that are faint compared to the sky. The actual details of obtaining and combining the images are the sub ject of endless debate. Sky exposures need to be taken close in time to the ob ject exposures as the sky background changes rapidly, but exactly how rapidly depends on the night. It is best to do quick sky subtractions as you observe to get an idea for this. A typical sequences might be four ob ject exposures interspersed with four sky exposures in an ABBAABBA sequence. The sky exposures would have their bias subtracted and then be linearized. They would be combined to form a single sky image, perhaps with multiplicative adjustment to the same median and outlier rejection to eliminate stars. The ob ject exposures would have their bias subtracted and be linearized. The sky exposure would be subtracted from each. Since the sky is variable even on short timescales, the ob ject exposures will often have some residual sky emission which needs to be removed by subtracting a constant. The o sets between the ob ject exposures need to be determined and the images shifted and combined. When combining ob ject images you need to deal with both bad pixels and spurious values in normally good pixels (from electronic glitches and particle events). A good method is to use a bad pixel mask to deal with the persistently 37


bad pixels and outlier rejection to deal with spurious values.

38


Chapter 6

Spectroscopy
6.1 Capabilities
GRIM II can be used as a low resolution spectrograph by placing a grism in the beam. The J , H , and K windows can be selected by using the J , H , and K lters. The K band is at 3rd order, the H band at 4th order, and the J band at 5th and 6th order, which unfortunately overlap. The resolution can be selected between = of about 200, 400, and 800 by using the f=5, f=10, and f=20 cameras with 240, 120, and 60 m slits. The (design) e ective focal length of the 3.5m is 35.24m. Thus, the slits have widths of 1.40, 0.70, and 0.35 arcsec on the sky. Three 60 m slits are provided to cover the entire K window. Table 6.1 shows the wavlength coverage of the di erent con gurations.
This chapter is incomplete.

6.2 Flat Fields
Lights on/o at elds can be obtained using the bright quartz lamps.

6.3 Wavelength Calibration
There are three common methods for obtaining a wavelength calibration: arc lamps, nigth sky lines, and emission line nebulae. Helium, neon, and argon lamps are available. Line lists for these can be found in the CRC. Long expsoures (of order 300s) are required and it is worthwile taking lights on/o exposures to remove thermal background. A good source of the wavelengths of airglow lines is Dick Joyce's manual for the KPNO CRSP spectrograph, available from the KPNO WWW page. For the high resolution work, the airglow lines are considered unreliable as many are blends, but they should be ne at the low resolution of GRIM II. Finally,bright emission line nebulae can be used, especially in the H window where many Br lines are visible. Some observers use 39


Camera & Slit f=5 f=10 f=20 Short f=20 Mid f=20 Long

Order 6 0.844{1.301 0.958{1.187 0.970{1.082 1.015{1.127 1.068{1.180

Order 5 1.013{1.561 1.150{1.424 1.163{1.298 1.217{1.352 1.282{1.415

Order 4 1.266{1.951 1.437{1.780 1.454{1.622 1.522{1.690 1.602{1.769

Order 3 1.688{2.602 1.916{2.373 1.939{2.163 2.029{2.253 2.136{2.359

Table 6.1: Wavelength Coverage in m

40


these lines to obtain a good solution in the H window and then use the grating equation to transfer to other orders.

6.4 Absorption Standards
Good sources of B and A stars for absorption standards are the Bright Star Catalog, SIMBAD, or the Tycho/Hipparchos Input Catalog. Kurucz stellar atmospheres can be used to model their intrinsic spectra. Late-type stars are sometimes used for programs that require good cancelation in the vicinity of hydrogen lines (see the discussion in the appendix of Hanson, Conti, & Rieke 1997). Alternatively, one can simply interpolate over the Br feature.

41


Chapter 7

Extinction
The atmospheric extinction above1 m results largely from molecular absorption and shows signi cantvariations as the water vapour content of the atmosphere changes from season to season, night to night, and even hour to hour. MODTRAN3 model transmittances at the zenith for APO in the summer and winter are shown in Figure 7.1. These models are the standard mid-latitude summer and winter atmospheres with no aerosol contribution. MODTRAN3 is the latest atmosphere radiation transfer code from the Air Force Phillips Laboratory. It is freely available from
ftp://146.153.100.3/pub/chet/

Most of the absorption results from molecular bands and many are saturated or semi-saturated. This means that the familar linear extinction law

m(X )= m(0) + CX

(7.1)

is invalid to some degree, as it assumes that the optical depth at all frequencies scales linearly with airmass. Instead, the true extinction law is non-linear. This problem is discussed in detail by Manduca & Bell (1979) and Young, Milone, & Stagg (1994). For normal di erential photometry between 1 and 2 airmasses the departures fron non-linearity are small (less than 1%) but increase at higher airmasses for absolute photometry the non-linearity can be much larger (tens of %). It is probably wise to avoid standard or ob ject exposures above an airmass of 2. Because the transmittance has so much structure, one cannot na vely apply extinctions derived by broad band observations to narrow band observations. If you do not wish to derive extinction coe cients for each narrow band lter you use, you should observe standards and ob jects at similar airmasses.

42


Figure 7.1: Model Atmospheric Transmitances

43


Chapter 8

Standards
8.1 Photometric Standards
Near infrared standards are immature compared to optical standards. There are many di erent standard systems (Johnson, Glass, CIT, CTIO, AAO, MSO, ESO, UKIRT, Carter) not all of which are especially well de ned. Glass (1985), Bessell & Brett (1988), and Carter (1993) discuss these systems and give transformations between them. The di erences between systems are smallest at K and largest at J . Most of these systems were constructed with InSb photometers in mind and are too bright to use with infrared array cameras on moderate-aperture telescopes (see x5.4). There are really only three choices of JH K standards for use with GRIM II: the Elias et al. standards, the Carter & Meadows standards, and the Casali & Hawarden standards. Each has advantages and disadvantages and you will have to select the one that matches your requirements for photometric accuracy and easy of use. The only K standards known to the author are the Wainscoat & Cowie standards. Observing your standards with a di erent instrumental con guration (e.g., a higher f= cameras or the neutral density lters) will probably introduce systematic errors in your photometry.
0

Ks

Does anyone have standards?

For many years the most commonly used standards suitable for the northern hemisphere have been those of Elias et al. (1982). These standards are on the CIT system, suitable for both hemispheres, and have a reasonable range of color. Unfortunately, even the `faint' standards have K 7 and are too bright to observe with GRIM II even at f=20 without defocusing. Many of these standards have high proper motions. Elias et al. also give CO and H2 O indices for many of their standards.

8.1.1 Elias et al. JH K , CO, and H2O Standards

An accurate measurementof the transformation would be useful.

44


8.1.2 Carter & Meadows JH K Standards

Carter & Meadows (1995) have de ned a slightly fainter set of standards on the Carter system with 8 ftp://oldp.nmsu.edu/pub/alan/ukirt.ps.Z

8.1.3 Casali & Hawarden JH K Standards

8.1.4 Wainscoat & Cowie K Standards
0 0 0 0

K magnitudes are di erent from K magnitudes, partly because the lter has

a shorter central wavelength and partly because it is less sensitive to the CO bands and more sensitive to the H2 O band in late-type stars. Wainscoat & Cowie (1992) de ne the K system and give K magnitudes for 18 of the Elias faint standards. They derive K ; K =(0:22 0:03)(H ; K ) (8.1) for unreddened dwarf stars. This transformation is not necessarily valid for giants, reddened stars, or galaxies. Nevertheless, some idea of the possible errors can be gained by applying this equation to the ob jects under consideration. Consider the case of observing the Casali & Hawarden standards (which have H ; K 0) and nearby galaxies (which have H ; K 0:3). The galaxies are expected to be 5{10% fainter in K relative to the standards than they are in K.
0 0

One possible solution to the lackof K standards is to `manufacture' a set from a set of JH K standards using the transformation given byWainscoat & Cowie (1992).
0

8.1.5 Manufactured K Standards
0

8.1.6 Absolute Calibration

Bessell & Brett (1988) derive an absolute calibration for JH K from the Vega optical absolute ux measurement and a model atmosphere. Campins, Rieke, & Lebofsky (1985) also derive a calibration using the solar analog method. 45


8.2 Spectrophotometric Standards
There are no empirical spectrophotometric standards in the near infrared all rely on model atmospheres to a greater or lesser extent.

8.2.1 Bohlin Spectrophotometric Standards

Bohlin (1996) presents four DA white dwarf photometric standards for use in the near infrared. The stars have K 13. Model atmosphere calculations provide the relative uxes and optical photometry sets the absolute ux. The accuracy of these standards in the near infrared is not well known, but some indication is given by the 3.5% disagreement between the two sets of models considered by Bohlin. Finding charts are presented by Bohlin, Colina, & Finley (1995). Note that HZ 43 has a close, red companion at a separation of only 3 arcsec this probably makes it unsuitable for use as a near infrared standard for ground-based observations. Again, spectrophotometric standards can be `manufactured' using broad band photometry, an absolute photometric calibration, and a model atmosphere or an observation from a spectral atlas. The e ective temperature scale of Code et al. (1976) and Kurucz model atmospheres can be used with early-type stars. The model solar spectrum presented by Colina, Bohlin, & Castelli (1996) can be used with solar analogs (e.g., those of Hardorp 1978, 1980, and 1982).

8.2.2 Manufactured Spectrophotometric Standards

8.3 Stellar Colours
The following studies of stellar colours may be useful: Koorrneef (1983) early- and late-type dwarfs, giants, and supergiants Bessell & Brett (1988) late-type dwarfs and giants Leggett (1992) late-type dwarfs

8.4 Stellar Spectra
The following studies of stellar spectra may be useful: Kleinmann & Hall (1996) R 3000 K late-type stars 46


Arnaud, Gilmore, & Collier Cameron (1989) R 100 K late-type stars Terndrup, Frogel, & Whitford (1991) R 1000 K local and bulge M giants Lancon & Rocca-Volmerange (1992) R 500 HK early- and late-type stars Kirkpatrick et al. (1993) R 300 J M dwarfs Origlia, Moorwood, & Oliva (1993) R 1500 H late-type stars Ali et al. (1995) R 1350 K late-type dwarfs Wallace et al. (1996) R 45000 JH K Sun Wallace & Hinkle (1996) R 300000 K late-type stars Hanson, Conti, & Rieke (1996) R 1000 K early-type stars Colina, Bohlin, & Castelli (1996) R 1250 JH K Sun largely based on a Kurucz model Leggett et al, (1996) R 250 JH K late-type dwarfs

47


Chapter 9

Headers
Certain information is placed into GRIM II images headers by the MC. The most useful header values are summarized in Table 9.1.

48


Name

IMTITLE OPENTIME STARTIME STOPTIME UT LT UTDATE RA DEC EPOCH RAOFF DECOFF X Y ROTATION ZD AIRMASS MODE SCALE GFILTER

Meaning Image name (without the .fits, .hhh,or .hhd extension) Exposure time ; 0:901 seconds (see x3.2) Time exposure started (local time) Time exposure stopped (local time) Time exposure was commanded (UTC) Time exposure was commanded (local time) Date of exposure (UT) Right Ascension Declination Epochof RA and DEC Ob ject o set in Right Ascension (arcsec) Instrument o set in Declination (arcsec) Instrument o set in y (arcsec) Instrument o set in y (arcsec) Instrument rotation (degrees) Zenith distance Airmass Mode value from Table 4.1 Scale value from Table 4.2 Filter value from Table 4.3 Table 9.1: Header Values

49


References
Ali, B., Carr, J. S., DePoy,D. L., Frogel, J. A., & Sellgren, K. 1995, AJ, 110, 2415 Arnaud, K. A., Gilmore, G., & Collier Camerson, A. 1989, MNRAS, 237, 495 Ashley, M. C. B., Burton, M. G., Storey,J. W. V., Lloyd,J.P., Bally,J., Briggs, J. W., & Harper, D. A. 1996, PASP, 108, 721 Bessell, M. S., & Brett, J. M. 1988, PASP, 100, 1134 Campins, H., Rieke, G. H., Lebofsky, M. J. 1985, AJ, 90, 896 Colina, L., Bohlin, R. C., & Castelli, F. 1996, AJ, 112, 307 Bohlin, R. C., Colina, L., & Finley, D. S. 1995, AJ, 101, 1316 Bohlin, R. C. 1996, AJ, 111, 1743 Carter, B. S. in Precision Photometry,eds. D. Kilkenny, E. Lastovica, & J. W. Menzies, (SAAO: Cape Town), p. 100 Carter, B. S., & Meadows, V. S. 1995, MNRAS, 276, 734 Casali, M., & Hawarden, T. 1992, JCMT-UKIRT Newsletter, 3, 33 Code, A. D., Javis, J., Bless, R. C., Hanbury Brown, R. 1976, ApJ, 203, 417 Elias, J. H., Frogel, J., Matthews, K., & Neugebauer, G. 1982, AJ, 87, 1029 (with erratum in AJ, 87, 1893) Glass, I. S. 1985, Irish AJ, 17, 1 Hanson, M. M., Conti, P. S., & Rieke, M. J. 1986, ApJS, 107, 281 Hardorp, J. 1978, A&A, 63, 383 Hardorp, J. 1980, A&A, 88, 334 Hardorp, J. 1982, A&A, 105, 120 50


Kirkpatrick, J. D., Kelly, D. M., Rieke, G. H., Liebert, J., & Allard, F., & Wehrse, R. 1993, ApJ, 402, 643 Kleinmann, S. G, & Hall, D. N. B. 1986, ApJS, 62, 501 Koornneef, J. 1983, A&A, 128, 84 Lancon, A., & Rocca-Volmerange, B. 1992, A&AS, 96, 593 Landolt, A. U. 1990, PASP, 102, 1382 Leggett, S. K. 1992, ApJS, 82, 351 Leggett, S. K., Allard, F., Berrimen, G., Dahn, C., C., & Hauschildt, P.H. 1996, ApJS, 104, 117 Manduca, A., & Bell, R. 1979, PASP, 91, 848 Nguyen, H. T., Rauscher, B. J., Severson, S. A., Hereld, M., Harper, D. A., Loewenstein, R. F., Mrozek, F., & Pernic, R. J. 1996, PASP, 108, 718 Origlia, L., Moorwood, A. F. M., & Oliva, E. 1993, A&A, 280, 536 Terndrup, D. M., Frogel, J. A., & Whitford, A. E. 1991, ApJ, 378, 742 Wainscoat, R. J., & Cowie, L. L. 1992, AJ, 103, 332 Wallace, L., & Hinkle, K. 1996, ApJS, 107, 281 Wallace, L., Livingston, W. Hinkle, K., & Bernath, P. 1996, ApJS, 106, 165 Young, A. T., Milone, E. F., & Stagg, C. R. 1994, A&AS, 105, 259

51


Index
absorption standards, 41 aperture stop, 3 bad pixels, 12 bias exposure, 6 IRAF bias, 6 variability,6 camera, 3 camera carousel, 3 collimator lens, 3 dark current, 6 exposure, 6 detector, 3, 5 bad pixels, 12 bias, 6 columns 128 and 256, 14 full well, 12 gain, 5 linearity,6 non-linearity,6 orientation, 3 peculiarities, 14 read noise, 5 residual image, 12 exposure time, 5 extinction, 42 absorption standards, 41 law, 42 non-linearity,42 eld of view, 25 lter wheel, 3 lters, 3, 16, 21, 49 2.17 m,35 characteristics, 25 focus shift, 28 K ,28 Kdark ,28 Ks ,28 neutral density, 3, 16, 21, 25, 49 transmittances, 25 at elds, 6, 35, 39 dome ats, 35 sky ats, 35 wavelength dependence, 6 focus, 19, 22, 28 FTP, 16, 20
0

grism,3,16, 21,39, 49 grism wheel, 3 hangs, 24 header value, 48 DEC,19, 49 DECOFF, 19, 49 EPOCH,49 GFILTER,16, 49 IMTITLE,49 LT,49 MODE, 16, 49 OPENTIME,5, 49 RA,19, 49 RAOFF,19, 49 ROTATION,19 ROTATTION,49 SCALE,16, 49 52

f ratio, 16, 25, 49
eld lens, 3


STARTIME,49 STOPTIME,49 UT,49 X,19, 49 Y,19, 49 ZD,49

imaging, 25 instrumental polarization, 3 lamps quartz, 37 linearity,6 mailing list, 2 MC, 5, 6, 15, 24 center procedure, 21 commands, 16 config procedure, 21 diskname command, 19 documentation, 15 east procedure, 21 end procedure, 21 example session, 23 exp procedure, 21 fexp procedure, 22 filetype command, 19 filter procedure, 21 focus command, 19 grimabort command, 16, 24 grimmove command, 16 grimstatus command, 16 home procedure, 22 imdir command, 19 inst command, 16 loginftp command, 20 mode procedure, 21 nexpose command, 16 north procedure, 21 obj1 procedure, 21 obj4 procedure,22 offset command, 19 places command, 19 priority command, 16 procedures, 15, 20 rotate command, 19 53

session, 15 slew command, 16 south procedure, 21 start procedure, 21 status display,15 stop command, 19 subscribe command, 20 west procedure, 21 mcnode UNIX command, 15 mode, 16, 21, 49 MODTRAN3, 42 non-linearity,6 optical layout, 3 orientation, 25 pixel scale, 25 REMARK, 5, 15, 24 documentation, 15 residual image, 12 response uniformity,6 saturation, 12 scale, 16, 21, 49 shutter, 5 slit wheel, 3 spectroscopy,39 standards, 44 absolute calibration, 45 Bohlin, 46 Carter & Meadows, 45 Casali & Hawarden, 45 CO, 44 Elias, 44 H2 O, 44 JH K ,44, 45 K ,45 manufactured, 45 photometric, 44 spectrophotometric, 46 Wainscoat & Cowie, 45 stellar colours, 46 stellar spectra, 46
0

scale procedure, seq command, 19

21


TCL, 20 user's manual, 1 wavelength calibration, 39

54