Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.stsci.edu/hst/wfc3/documents/meeting_posters/spie_2014/Deustua_Poster_SPIE_2014.pdf Äàòà èçìåíåíèÿ: Unknown Äàòà èíäåêñèðîâàíèÿ: Tue Apr 12 06:22:23 2016 Êîäèðîâêà:

HST/WFC3 Flux Calibration Ladder: Vega
Susana E. Deustua,, Ralph Bohlin, Nor Pirzkal & John MaKenty. Space Telescope Science Institute (United States)

Operated for NASA by AURA

SP CE A TELESCOPE SCIENCE INSTITUTE

electrons/sec

! ! ! Vega is the quintessential absolute flux calibrator in Astronomy, and, ! one of only a few stars calibrated against an SI-traceable blackbody. The ! majority of experiments made measurements the visible (see Megessier ! 8·10 Vega: coadded spectra G141 1995 for a detailed discussion) with uncertainties on the order of a few ! percent. Equivalent measurements made in the infrared, from the 6·10 ! ground, yielded much larger uncertainties (e.g. Blackwell and 4·10 collaborators), due in large part to atmospheric effects. Hence, Figure 1. Positions on the detector of the spectral scans. Grism orders accurate measurements made above the atmosphere should reduce the 2·10 from right to left are +2nd, +1st, 0th, -1st and -2nd. Left: 0th, -1st, -2nd. Slivers of the +1st on the right edge, and -3rd on the left edge are visible. uncertainties! Center: +1st, 0th, -1st and -2nd orders. Right: +2nd, +1st, 0th and -1st 0 1.6 orders a1.0 visib1.2 The1.4 , +1st and1.8 nd orders are saturated! re le. 0th +2 ! Wavelength (microns) STIS spectral observations of Vega between 3000 angstroms and 1 Vega: coadded spectra G141 Vega: coadded spectra G102 8·10 6·10 micron were made by Bohlin and Gilliland (2004, AJ, 127, 3508 ) in the traditional stare mode. By exploiting the fact that in the STIS CCD 6·10 4·10 saturated charge in one pixel spills over to neighboring pixels, thereby 4·10 conserving flux, they were able to obtain high signal to noise spectra of 2·10 2·10 this fundamental flux standard. ! ! 0 0 1.0 1.2 1.4 1.6 1.8 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 At wavelengths longer than 1 micron Vega's spectral energy Wavelength (microns) Wavelength (microns) distribution is obtained by extrapolating from the current UVIS data via Figure 2 Coadded unfluxed spectra of Vega Vega: h scan rate for thG102 orders at eac coadded spectra e -1st 6·10 models. To fill in the crucial gap between 0.9 and 1.7 microns, we of the G141 (top) and G102 (bottom) WFC3 IR grisms. Wavelength scale is in microns, negative numbers indicate negative order. Solid lines are the slow scan started a program to acquire grism spectroscopy of Vega in the near rates; dashed lines are the fast scan4·10 Top: Paschen is the dip at -1.28 s. microns, and the series of features between 1.6 and 1.7 microns are Br 13,12, infrared using the two Wide Field Camera 3 (WFC3) infrared grisms, in 11. Bottom: Pa is just visible at 1.09 microns, and Pa at 1.05 microns.! scanning mode. In principle we should obtain an absolute flux calibration 2·10 of less than 3%! ! 0 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 Spectra of Vega are obtained with spatial scanning in the -1st and, Wavelength (microns) depending on position on the array, the -2nd order. ! ! Calibration ! ! ! P330E model spectrum ! Cautions! ! -1st order calibrations. Because use of the -1st grism orders was not anticipated, these were not as we!ll calibrated as the +1st and +2nd orders. Therefore, we obtained +1st and -1st spectra of the sol!ar analog flux standard star P330E to check the flux calibration of the -1st order, and G141 +1st order ob ! rvations of the planetary nebula, VY2-2, to check the wavelength calibration.! se uncorrected spectrum ! ! Upstream/Downstream effects. Scans were made along the columns, either parallel to or opposite the scan direction. The effect is different scan lengths, and therfore different per pixel on source exposure times during one image. The WFC3/IR detector is readout using non destructive reads.
8

Introduction!

Vega Infrared Spectra!
6·10
DN/sec for V-ALF-LYR
8

G141 ibtw01

4·10

8

2·10

8

Flux (electrons/sec)

8

0 -1.8
wfc_coadd 2-Jan-2013 23:14:48.00

-1.6

8

-1.4 -1.2 -1.0 Wavelength (microns)

-0.8

-0.6

8

Figure 3. Visit 01; slow scan, -1st order spectra in G141 coadded at each scan position, after dark subtraction, flatfielding, dispersion correction and rectification. Note the 10% variation in the counts rates at wavelengths longer than 1.2 microns (left side of the plot). This is likely due to flat field variations.!

8

8

Flux (electrons/sec)

Flux (electrons/sec)

8

8

8

8

8

8

Flux (electrons/sec)

8

Figure 4. Comparison of GD71 and Vega spectra showing the wavelength calibration of the -1st order is comparable to the +1st order (inset).

8

1·10 8·10

-14

P330E Spectra

of -1st orders
Band 1: 1.15 - 1.32 microns
1.034 1.002 1.000 1.017 1.003 -1st order 200 400 600 X Pixels 1.031 1.025 1000 800

Band 2: 1.32- 1.4 microns
0.975 1.008 1.000 1.041 0.981 -1st order 200 400 600 X Pixels 0.461 1.249 1.000 0.264 1.158 200 400 600 X Pixels 800 1000 1.036 1.057 1.000 1.033 1.006 +1st order 800 1000

Flux (ergs/s/cm^2/Angstrom)

-15

1000 800 600 400 200 0 0

6·10

-15

4·10

-15

Y Pixels

Y Pixels Y Pixels

2·10

-15

1.000 1.029 0.995 +1st order 800 1000

600 400 200 0 0

0 1.0

1.2

1.4 Wavelength (microns)

1.6

1.8

60

electrons/sec

40

Band 3: 1.48 - 1.65 microns
0.988 0.997 1.000 1.000 0.998 -1st order 200 400 600 X Pixels 1.032 1.044 1.000 1.000 1.001 +1st order 800 1000

1.15 - 1.65 microns, 0th Order
1000 800 600 400 200 0 0

20

1000 800 600 400 200 0 0

0 1.0

1.2

1.4 Wavelength (microns)

1.6

1.8

0.8 0.6

0.4

0.2

G141 -1st order uncorrected spectrum

0.0 -0.2 1.0

1.2

1.4 Wavelength (microns)

1.6

1.8

Y Pixels

!! ! The measured scan ! length is a function of ! the scan rate, the ! sample time (time ! between reads) and the ! time to readout the ! array. Our spectra were ! tained using the ob ! PID sample sequence RA which has uniform intervals of 2.93 seconds between reads. The time to readout one quadrant is 2.91 seconds. !

Upstream/Downstream Effect!

Figure 1. Top panel: P330E model spectrum in the IR extended from STIS spectra. Middle and Bottom panels show coadded WFC3/IR G141 spectra after flat fielding, sky subtraction, and dispersion correction. Flux units are electrons/ second.!

Figure 3. Variation in sensitivity in 3 wavelength ranges over the array with respect to the spectra in the middle position. Red points are obtained from the -1st order spectrum, blue points are from the +1st order. These are consistent with the results from Lee et al 2013!
Ratio of -1st to +1st order at Postion 1 for P330E
0.04 0.03
ratio

Ratio of -1st to +1st order at Postion 2 for P330E
0.04 0.03

ratio of spectra

0.01 0.00 -0.01 1.1·104 1.2·104 1.3·104 1.4·104 1.5·104 1.6·104 1.7·10 Wavelength (angstroms)
4

ratio

0.02

0.02 0.01 0.00 -0.01 1.1·104 1.2·104 1.3·104 1.4·104 1.5·104 1.6·104 1.7·10 Wavelength (angstroms)
4

residual wrt array average

Ratio of -1st to +1st order at Postion 3 for P330E
0.04 0.03
ratio ratio

Ratio of -1st to +1st order at Postion 4 for P330E
0.04 0.03 0.02 0.01 0.00 -0.01

0.02 0.01 0.00 -0.01 1.1·104 1.2·104 1.3·104 1.4·104 1.5·104 1.6·104 1.7·10 Wavelength (angstroms)
4

1.1·104 1.2·104 1.3·104 1.4·104 1.5·104 1.6·104 1.7·10 Wavelength (angstroms)

4

Ratio of -1st to +1st order at Postion 5 for P330E
0.04 0.03
ratio ratio

Average Ratio over all Positions for P330E
0.04 0.03 0.02 0.01 0.00 -0.01

0.02 0.01 0.00 -0.01 1.1·104 1.2·104 1.3·104 1.4·104 1.5·104 1.6·104 1.7·10 Wavelength (angstroms)
4

Left Figure: Measured length of a readout direction are the same (pa other.! ! Right Figure: Ratios of measured time were instantaneous. Best fit second.

scan (in pixels) during one read when the scan direction and the rallel), and when the scan and readout direction are opposite each parallel and opposite scan lengths to expected length if readout lines are forced to include the values at scan rate= 0 arcsec/

1.1·104 1.2·104 1.3·104 1.4·104 1.5·104 1.6·104 1.7·10 Wavelength (angstroms)

4

Figure 2. Derived sensitivity functions for the two orders. Black curves are the values at launch.!

Figure 4. Ratios of the -1st to +1st spectra at! each of 5 positions, with residuals (blue curves) with respect to the average shown in the lower right panel. On average, the throughput of the -1st order is 100 times less sensitive.!