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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 (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). 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). 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:
FileName Lrecl Records Explanations
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
Byte-by-byte Description of file: stars.dat
Bytes Format Units Label Explanations
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
Byte-by-byte Description of file: tablea3.dat tablea4.dat tablea5.dat
Bytes Format Units Label Explanations
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
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.
Byte-by-byte Description of file: tableb1.dat tableb2.dat tableb3.dat
Bytes Format Units Label Explanations
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
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
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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