文档库

最新最全的文档下载
当前位置:文档库 > 1998. The American Astronomical Society. All rights reserved. Printed in U.S.A. INITIAL ON

1998. The American Astronomical Society. All rights reserved. Printed in U.S.A. INITIAL ON

The Astrophysical Journal,492:L95–L97,1998January10

᭧1998.The American Astronomical Society.All rights reserved.Printed in U.S.A.

INITIAL ON-ORBIT PERFORMANCE OF NICMOS

Rodger I.Thompson,Marcia Rieke,Glenn Schneider,Dean C.Hines,and Michael R.Corbin Steward Observatory,933North Cherry Avenue,University of Arizona,Tucson,AZ85721-0065

Received1997July23;accepted1997October30;published1997December30

ABSTRACT

On1997February13,Space Shuttle astronauts placed the Near-Infrared Camera and Multiobject Spectrometer (NICMOS)into the Hubble Space Telescope.Following installation,the servicing mission orbital verification program(SMOV)performed extensive testing of the instrument to verify that it can be operated and calibrated effectively.This program is essentially completed,and routine science observations have begun in most of the NICMOS modes of operation.This Letter describes the performance levels of NICMOS at this time.

Subject headings:instrumentation:detectors—miscellaneous—space vehicles

1.INTRODUCTION

The Near-Infrared Camera and Multiobject Spectrometer (NICMOS)provides imaging,spectroscopic,polarimetric,and coronagraphic observations in the near-infrared(1.0–2.5m m) with the Hubble Space Telescope(HST).Its primary purpose is to get diffraction-limited,high-resolution imaging throughout the spectral region and to exploit the lack of strong telluric OH emission at the HST orbital altitude.Experience with the Ϫ

NICMOS3infrared detectors developed for the mission in-dicated a response at wavelengths as short as0.8m m;therefore,filters were added to utilize this capability.This provides an overlap with the Wide Field Planetary Camera(WFPC)and Space Telescope and Imaging Spectrograph(STIS)wave bands for linking observations from the ultraviolet to the near-infra-red.The thermal emission from the warm HST mirrors limits observations beyond2.5m m,and so the detectors were tuned to cut off at that wavelength.Details of the instrument and its operation are given by MacKenty et al.(1997).

2.IMAGING PERFORMANCE

We have excellent image performance data on the high-resolution cameras1and2from the servicing mission orbital verification(SMOV)activities.In-focus,image-quality data are not available for the WFPC3since it is not currently within the range of the NICMOS focus adjustment mechanism.How-ever,we do have a good characterization of the detector per-formance parameters,which are discussed in§2.2.Table1 gives the imaging characteristics of the three cameras.The difference between the X and Y pixel scales is due to the tilt of the image plane at the location of the detectors.This is primarily due to the off-axis placement of NICMOS.The dif-ference was not considered significant enough to tilt the de-tectors in compensation for thefield angle.

2.1.Image Quality

The observed image quality in cameras1and2match well with the expected image quality.Figure1compares the encir-cled energy as a function of radial distance for a point-spread function(PSF)computed using the software program TINY TIM(Krist1995)and the encircled energy measured for a star image in camera2.Thefilter was the broadbandfilter F160W, which has a center wavelength slightly shorter than the camera 2diffraction limit wavelength of1.75m m.We define the dif-fraction limit as the wavelength where the camera has5pixels between thefirst zeros of the theoretical PSF for HST.Figure

1shows that the actual encircled energy function is very close to the theoretical function.Figure2(Plate L5)compares the TINY TIM synthetic image with the camera2F160Wfilter image of an actual star observed with NICMOS.The only differences are attributable to the actual star image not being exactly centered on a pixel.

This special issue of the Astrophysical Journal Letters con-tains several plates andfigures that demonstrate the image qual-ity of the NICMOS cameras.As an example,note the plates in Stolovy et al.(1998),where the Airy rings of the diffraction pattern are well defined in the brighter stars in the plate.Also note the detection of several faint stars3Љ–4Љaway from a bright source nearly104times brighter in Thompson et al.

(1998).This clearly shows the low scattering background in NICMOS and the advantages of detectors that do not leave trails of residual image near very bright objects because of charge transfer effects.

2.2.Photometric Performance

The photometric performance of NICMOS is close to the prelaunch estimates of the NICMOS instrument definition team.

At this time,the Exposure Time Calculation tool maintained by the Space Telescope Science Institute(STScI)is undergoing

a revision to reflect the true on-orbit performance of the in-

strument.Table1gives some of the basic photometric para-meters for three cameras.These include the dark current,read noise,and gain.On-orbit measurements show that the back-ground infraredflux levels are less than the levels expected beforeflight.This means that the cold baffling of the detectors is working well and that there are no unexpected thermal sources in the HST itself.

To date,none of the basic parameters such as noise,dark current,or gain have changed while in orbit.In a period of3 months of monitoring in orbit,there has been no change in the dark current attributable to the action of cosmic rays on the detector.There also has been no change in the number of elec-trically bad pixels attributable to cosmic-ray damage.

The total photometric performance is a combination of all of the photometric parameters.SMOV activities included pho-tometric tests in selectedfilters.The tests produced images of

a standard star at three different locations on the array in four

tofivefilters per camera.Table2gives the performance levels of the cameras in the measuredfilters along with the expected sensitivity for a1000s integration on a point source.The sensitivity number is expressed as theflux of a point source in units of janskys that will give a signal-to-noise(S/N)ratio

L95

# 2007. The American Astronomical Society. All rights reserved. Printed in U.S.A. THE SUN-L

# 2007. The American Astronomical Society. All rights reserved. Printed in U.S.A. THE SUN-L_专业资料。We present the results of 10 yr of ...

1999. The American Astronomical Society. All rights reserved. Printed in U.S.A. THE FORNAX

The American Astronomical Society. All rights reserved. Printed in U.S.A....Sadler7 Received 1998 August 21; accepted 1998 November 24; published 1998 ...

1999. The American Astronomical Society. All rights reserved. Printed in U.S.A. RANDOM-LAG

1999. The American Astronomical Society. All rights reserved. Printed in U.S.A. RANDOM-LAG SINGULAR CROSS-SPECTRUM ANALYSIS F. Varadi,1 R. K. Ulrich...

2001. The American Astronomical Society. All rights reserved. Printed in U.S.A. SUBSTRUCTU

2001. The American Astronomical Society. All rights reserved. Printed in U.S.A. SUBSTRUCTU_专业资料。We present the first dynamical analysis of a galaxy...

2006. The American Astronomical Society. All rights reserved. Printed in U.S.A. MEASUREMEN

2006. The American Astronomical Society. All rights reserved. Printed in U.S.A. MEASUREMEN_专业资料。We present spectroscopy of a transit of the exo...

# 2003. The American Astronomical Society. All rights reserved. Printed in U.S.A. WHAT CAUS

# 2003. The American Astronomical Society. All rights reserved. Printed in U.S.A. WHAT CAUS_专业资料。The solar acoustic p-mode line profiles are ...

2007. The American Astronomical Society. All rights reserved. Printed in U.S.A. VOLATILE L

2007. The American Astronomical Society. All rights reserved. Printed in U.S.A. VOLATILE L_专业资料。Recent discoveries have shown that the very largest...

2006. The American Astronomical Society. All rights reserved. Printed in U.S.A. WATER ICE

2006. The American Astronomical Society. All rights reserved. Printed in U.S.A. WATER ICE_专业资料。We have obtained a near-infrared spectrum of the ...

2007. The American Astronomical Society. All rights reserved. Printed in U.S.A. FEATURES A

The American Astronomical Society. All rights reserved. Printed in U.S.A....1998, ApJ, 503, 467 Forbes, T. G., & Malherbe, J. M. 1991, Sol....

1999. The American Astronomical Society. All rights reserved. Printed in U.S.A. NICMOS IMA

The American Astronomical Society. All rights reserved. Printed in U.S.A....Thompson,1 and Marcia Rieke1 Received 1998 November 24; accepted 1999 ...