J/AJ/149/11 Spectra of candidate standard stars in mid-IR (Sloan+, 2015)
Spectral calibration in the mid-infrared: Challenges and solutions
Sloan G.C., Herter T.L., Charmandaris V., Sheth K., Burgdorf M., Houck J.R.
<Astron. J. 149, 11 (2015)>
=2015AJ....149...11S 2015AJ....149...11S
ADC_Keywords: Spectra, infrared - Stars, A-type - Stars, K-type - Spectral types
Keywords: infrared: stars
Abstract:
We present spectra obtained with the Infrared Spectrograph (IRS) on
the Spitzer Space Telescope of 33 K giants and 20 A dwarfs to assess
their suitability as spectrophotometric standard stars. The K giants
confirm previous findings that the strength of the SiO absorption band
at 8µm increases for both later optical spectral classes and redder
(B-V)0 colors, but with considerable scatter. For K giants, the
synthetic spectra underpredict the strengths of the molecular bands
from SiO and OH. For these reasons, the assumed true spectra for K
giants should be based on neither the assumption that molecular band
strengths in the infrared can be predicted accurately from optical
spectral class or color nor synthetric spectra. The OH bands in K
giants grow stronger with cooler stellar temperatures, and they are
stronger than predicted by synthetic spectra. As a group, A dwarfs are
better behaved and more predictable than the K giants, but they are
more likely to show red excesses from debris disks. No suitable A
dwarfs were located in parts of the sky continuously observable from
Spitzer, and with previous means of estimating the true spectra of K
giants ruled out, it was necessary to use models of A dwarfs to
calibrate spectra of K giants from observed spectral ratios of the two
groups and then use the calibrated K giants as standards for the full
database of infrared spectra from Spitzer. We also describe a
lingering artifact that affects the spectra of faint blue sources at
24µm.
Description:
The first set of usable observations of standard stars came in the
Infrared Spectrograph (IRS) Campaign P, which was executed 2003
November 14-16. Normal operations began on 2003 December 14, and every
IRS campaign from then until cryogens were exhausted on 2009 May 15.
This dataset includes 53 spectra observed with the Infrared
Spectrograph (IRS) on the Spitzer Space Telescope, along with the two
truth spectra used to calibrate the rest of the data (for the K giants
HR 6348 and HD 173511). The spectra were obtained with the
low-resolution modules (Short-Low and Long-Low, which obtained spectra
with resolutions λ/Δλ of roughly 80-120) on the
IRS and cover wavelengths of 5 to 37µm. Two tables providing
details of the sources are also included, one for the 33 K giants and
the other for the 20 A dwarfs.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 96 33 The sample of 33 K giants
table3.dat 94 20 The sample of 20 A dwarfs
refs.dat 171 23 References
sp/* . 53 Spectral data
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Byte-by-byte Description of file: table[23].dat
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Bytes Format Units Label Explanation
--------------------------------------------------------------------------------
1-10 A10 --- Name Name of target used in filenames,
in subdirectory sp
12-15 I4 --- HR [1014/8585]? Harvard Revised (V/50) number
17-22 I6 --- HD [15508/214873]? Henry Draper (III/135) number
24-29 I6 --- HIP [11364/175510] Hipparcos catalog (I/239) number
31-32 I2 h RAh Hour of Right ascension (J2000)
34-35 I2 min RAm Minute of Right ascension (J2000)
37-41 F5.2 s RAs Second of Right ascension (J2000)
43 A1 --- DE- Sign of the Declination (J2000)
44-45 I2 deg DEd Degree of Declination (J2000)
47-48 I2 arcmin DEm Arcminute of Declination (J2000)
50-53 F4.1 arcsec DEs Arcsecond of Declination (J2000)
55-62 A8 --- SpT1 Spectral type from the literature
64-74 A11 --- r_SpT1 References for spectral type (the listed
references are not meant to be complete);
in refs.dat file
76 A1 --- f_SpT2 [b] Indicates that the SpT2 differs from the
spectral class in the SpT1 column
78-79 A2 --- SpT2 Modified spectral class (only in Table 2) (1)
81 A1 --- f_S12 [c] 12µm flux from IRAS PSC (2)
83-87 F5.3 Jy S12 IRAS flux density Sν at 12µm (3)
89-91 I3 --- No [1/132] Number of Infrared Spectrograph (IRS)
observations obtained
93-94 I2 --- Nu [1/84] Number of IRS observations used
96 A1 --- f_Name [T] "T" Indicates that the spectrum is a
template and not an IRS spectrum
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Note (1): See the Section 6.3 for details.
Note (2): S12 from the IRAS Point Source Catalog (FSC; Moshir,
1992ifss.book.....M 1992ifss.book.....M; see cat. II/338) and color-corrected as the
IRAS Faint-Source Catalog data.
Note (3): Photometry from the IRAS Faint-Source Catalog (FSC; Moshir,
1992ifss.book.....M 1992ifss.book.....M; see cat. II/338) and color-corrected by dividing by
1.45, unless noted otherwise.
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Byte-by-byte Description of file: refs.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 A6 --- Ref Reference code
8- 26 A19 --- BibCode BibCode
28- 45 A18 --- Aut Auhtor's naem
47-171 A125 --- Rem Remarks
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Byte-by-byte Description of file (#): sp/*
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Bytes Format Units Label Explanation
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2-8 F7.3 um lambda [5.127/42.267] Wavelength λ
14-22 E9.3 Jy Snu [0/5.5] Flux density Sν
25-33 E9.3 Jy e_Snu Uncertainty in flux density
36-38 I3 --- order [1/6] Unique identifier for the spectral segment
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Acknowledgements:
Gregory C. Sloan, sloan(at)isc.astro.cornell.edu
(End) G. C. Sloan [Cornell Univ., USA] 27-May-2015