J/A+A/613/A40 PACS photometry of FIR faint stars (Klaas+, 2018)
Herschel-PACS photometry of faint stars for sensitivity performance assessment
and establishment of faint FIR primary photometric standards.
Klaas U., Balog Z., Nielbock M., Mueller T.G., Linz H., Kiss Cs.
<Astron. Astrophys. 613, A40 (2018)>
=2018A&A...613A..40K 2018A&A...613A..40K (SIMBAD/NED BibCode)
ADC_Keywords: Stars, late-type ; Stars, giant ; Photometry, infrared ;
Space observations
Keywords: space vehicles: instruments - methods: data analysis -
techniques: photometric - infrared: stars - stars: atmospheres -
radiation mechanisms: thermal
Abstract:
Our aims are to determine flux densities and their photometric
accuracy for a set of seventeen stars that range in flux from
intermediately bright (≲2.5Jy) to faint (≳5mJy) in the far-infrared
(FIR). We also aim to derive signal-to-noise dependence with flux and
time, and compare the results with predictions from the Herschel
exposure-time calculation tool.
We obtain aperture photometry from Herschel-PACS high-pass-filtered
scan maps and chop/nod observations of the faint stars. The issues of
detection limits and sky confusion noise are addressed by comparison
of the field-of-view at different wavelengths, by multi-aperture
photometry, by special processing of the maps to preserve extended
emission, and with the help of large-scale absolute sky brightness
maps from AKARI. This photometry is compared with flux-density
predictions based on photospheric models for these stars. We obtain a
robust noise estimate by fitting the flux distribution per map pixel
histogram for the area around the stars, scaling it for the applied
aperture size and correcting for noise correlation.
Description:
70, 100 and 160um photometry of FIR faint stars from PACS scan map
and chop/nod measurements. For scan maps also the photometry of the
combined scan and cross-scan maps (at 160um there are usually two
scan and cross-scan maps each as complements to the 70 and 100um
maps) is given.
Note: Not all stars have measured fluxes in all three filters.
Scan maps:
The main observing mode was the point-source mini-scan-map mode;
selected scan map parameters are given in column mparam.
An outline of the data processing using the high-pass filter (HPF)
method is presented in Balog et al. (2014ExA....37..129B 2014ExA....37..129B).
Processing proceeded from Herschel Science Archive SPG v13.1.0 level 1
products with HIPE version 15 build 165 for 70 and 100um maps and from
Herschel Science Archive SPG v14.2.0 level 1 products with HIPE
version 15 build 1480 for 160um maps.
Fluxes faper were obtained by aperture photometry with aperture radii
of 5.6, 6.8 and 10.7 arcsec for the 70, 100 and 160um filter,
respectively.
Noise per pixel sigpix was determined with the histogram method,
described in this paper, for coverage values greater than or equal to
0.5*maximum coverage.
The number of map pixels (1.1, 1.4, and 2.1 arcsec pixel size,
respectively) inside the photometric aperture is
Naper = 81.42, 74.12, and 81.56, respectively.
The corresponding correction factors for correlated noise are
fcorr = 3.13, 2.76, and 4.12, respectively.
The noise for the photometric aperture is calculated as
sig_aper=sqrt(Naper)*fcorr*sigpix.
Signal-to-noise ratios are determined as S/N=faper/sigaper.
Aperture-correction factors to derive the total flux are
caper = 1.61, 1.56 and 1.56 for the 70, 100 and 160um filter,
respectively.
Applied colour-correction factors for a 5000K black-body SED are
cc = 1.016, 1.033, and 1.074 for the 70, 100, and 160um filter,
respectively.
The final stellar flux is derived as fstar=faper*caper/cc.
Maximum and minimum FWHM of the star PSF are determined by an
elliptical fit of the intensity profile.
Chop/nod observations:
The chop/nod point-source mode is described in this paper.
An outline of the data processing is presented in Nielbock et al.
(2013ExA....36..631N 2013ExA....36..631N).
Processing proceeded from Herschel Science Archive SPG v11.1.0 level 1
products with HIPE version 13 build 2768.
Gyro correction was applied for most of the cases to improve the
pointing reconstruction performance.
Fluxes faper were obtained by aperture photometry with aperture radii
of 5.6, 6.8 and 10.7 arcsec for the 70, 100 and 160um filter,
respectively.
Noise per pixel sigpix was determined with the histogram method,
described in this paper, for coverage values greater than or equal to
0.5*maximum coverage.
The number of map pixels (1.1, 1.4, and 2.1 arcsec pixel size,
respectively) inside the photometric aperture is
Naper = 81.42, 74.12, and 81.56, respectively.
The corresponding correction factors for correlated noise are
fcorr = 6.33, 4.22, and 7.81, respectively.
The noise for the photometric aperture is calculated as
sigaper=sqrt(Naper)*fcorr*sigpix.
Signal-to-noise ratios are determined as S/N=faper/sigaper.
Aperture-correction factors to derive the total flux are
caper = 1.61, 1.56 and 1.56 for the 70, 100 and 160um filter,
respectively.
Applied colour-correction factors for a 5000K black-body SED are
cc = 1.016, 1.033, and 1.074 for the 70, 100, and 160um filter,
respectively.
Maximum and minimum FWHM of the star PSF are determined by an
elliptical fit of the intensity profile.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
stars.dat 33 17 List of FIR faint stars
tablea3.dat 110 113 PACS 70um scan map photometry of FIR faint stars
tablea4.dat 110 112 PACS 100um scan map photometry of FIR faint stars
tablea5.dat 110 175 PACS 160um scan map photometry of FIR faint stars
tableb1.dat 86 34 PACS 70um chop/nod photometry of FIR faint stars
tableb2.dat 86 24 PACS 100um chop/nod photometry of FIR faint stars
tableb3.dat 86 32 PACS 160um chop/nod photometry of FIR faint stars
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Byte-by-byte Description of file: stars.dat
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Bytes Format Units Label Explanations
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1- 2 I2 h RAh Simbad right ascension (J2000)
4- 5 I2 min RAm Simbad right ascension (J2000)
7- 11 F5.2 s RAs Simbad right ascension (J2000)
13 A1 --- DE- Simbad declination sign (J2000)
14- 15 I2 deg DEd Simbad declination (J2000)
17- 18 I2 arcmin DEm Simbad declination (J2000)
20- 23 F4.1 arcsec DEs Simbad declination (J2000)
25- 33 A9 --- Name Star name
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Byte-by-byte Description of file: tablea3.dat tablea4.dat tablea5.dat
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Bytes Format Units Label Explanations
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1- 22 A22 --- OBSID Herschel individual observation ID or
combination of IDs
24- 27 I4 --- OD Herschel Operational Day
29- 37 A9 --- Name Star name
39 A1 --- gain [h/l] PACS bolometer gain setting h(igh)/l(ow)
41- 42 I2 arcsec/s Speed Herschel telescope scan speed
44- 45 I2 --- Rep No. of scan map repetitions
47- 49 I3 arcsec Length Parameter of scan map, scan leg length
50 A1 --- --- [/]
51- 52 I2 arcsec Sep Parameter of scan map, scan leg separation
53 A1 --- --- [/]
54- 55 I2 --- Nlegs Parameter of scan map, number of scan leg
57- 62 A6 deg Sangle Orientation(s) of detector array
wrt. scan direction
64- 69 F6.1 mJy Faper Flux measured inside photometric aperture
71- 75 F5.3 mJy sigpix 1 sigma noise per pixel (1)
77- 81 F5.2 mJy e_Faper 1 sigma noise for photometric aperture
including correction for correlated noise (1)
83- 86 A4 --- S/N Signal-to-noise ratio of flux measurement (1)
88- 93 F6.1 mJy Fstar Stellar flux (color corrected)
95- 99 F5.2 arcsec Wmax Maximum FWHM of elliptical fit to PSF
101-105 F5.2 arcsec Wmin Minimum FWHM of elliptical fit to PSF
107-110 F4.2 arcsec Wunc Uncertainty of elliptical fit to PSF
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Note (1): After OD 1375 half of the red photometer array was lost, resulting
in increased noise sigpix, sigaper and reduced S/N wrt. pre-OD 1375
160um observations.
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Byte-by-byte Description of file: tableb1.dat tableb2.dat tableb3.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- OBSID Herschel individual observation ID
12- 21 F10.6 --- OD Herschel Operational Day plus fraction
23- 31 A9 --- Name Star name
33 A1 --- gain [h/l] PACS bolometer gain setting: h(igh)/l(ow)
35 A1 --- Dither [y/n] Chopper dither pattern: y(es)/n(o)
37- 38 I2 --- Rep No. of chop/nod pattern repetitions
40- 45 F6.3 mJy Fpeak Fitted peak flux
47- 52 F6.1 mJy Faper Flux measured inside photometric aperture
54- 58 F5.3 mJy sigpix 1 sigma noise per pixel
60- 63 F4.1 mJy e_Faper 1 sigma noise for photometric aperture
including correction for correlated noise
65- 67 A3 --- S/N Signal-to-noise ratio of flux measurement
69- 74 F6.1 mJy Fstar Stellar flux (color corrected)
76- 80 F5.2 arcsec Wmax Maximum FWHM of elliptical fit to PSF
82- 86 F5.2 arcsec Wmin Minimum FWHM of elliptical fit to PSF
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Acknowledgements:
Ulrich Klaas, klaas(at)mpia.de, Max-Planck-Institut fuer Astronomie
(End) U. Klaas [Max-Planck-Inst. Astron.], P. Vannier [CDS] 09-Jan-2018