| 1. |
|
|
| 2. |
- Dehaes, S., et al.
(författare)
-
SED for 7 stellar calibrators (Dehaes+, 2011)
- 2011
-
Ingår i: VizieR Online Data Catalog. ; 353
-
Tidskriftsartikel (refereegranskat)abstract
- This catalogue presents the theoretical spectral energy distributions for 7 stellar calibrators of the ESA Herschel satellite in the wavelength range from 2 to 200 micron. The stellar atmosphere model and theoretical spectrum are generated using the MARCS theoretical stellar atmosphere code (Gustafsson et al., 1975A\ampA....42..407G and further updates; Gustafsson et al. 2003A\ampA...400..709D) and the TURBOSPECTRUM synthetic spectrum code (Plez et al., 1992A\ampA...256..551P). Stellar parameters (and uncertainties thereon) have been derived by Decin et al. (2003A\ampA...400..709D) and are described in the text files added to this catalogue. The line lists used in the spectrum calculation are discussed in Decin (2000, PhD Thesis, Leuven University) and Decin and Eriksson (2007A\ampA...472.1041D). The outermost depth point of the theoretical atmosphere model was taken at log(tau$_lambda$)=-7.2 with lambda being 2.2 micron. The atmosphere model was calculated with a spherically symmetric (parallel for Sirius) geometry, under the assumption of radiative and hydrostatic equilibrium, local thermodynamic equilibrium (LTE) and homogeneous layers. The original theoretical spectrum was calculated at a resolution of Δλ=0.5Å, and then degraded to a resolution of λ/Δλ=5000 applying a gaussian convolution. The wavelength coverage is from 2 to 200 micron. Uncertainties on the theoretical spectrum predictions are discussed in depth in Decin \amp Eriksson (2007A\ampA...472.1041D). Absolute flux calibration is based on Selby (1988A\ampAS...74..127S) K-band (TCS for Sirius) photometry Zero-point is determined on the basis of an ideal ’Vega’, i.e. the K-band photometry of Vega is corrected for a flux excess of 1.29% (cf. Absil et al. 2006A\ampA...452..237A). The determined Selby K-band zeropoint is 4.0517E-10 W/m2/um. The determined TCS K-band zeropoint is 4.4506E-10W/m2/um (for Sirius) The estimated absolute flux uncertainty is 1% These theoretical spectra should be referenced as Decin \amp Eriksson (2007A\ampA...472.1041D). (3 data files).
|
|
| 3. |
- Dehaes, S., et al.
(författare)
-
Structure of the outer layers of cool standard stars
- 2011
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 533, s. A107-
-
Tidskriftsartikel (refereegranskat)abstract
- Context. Among late-type red giants, an interesting change occurs in the structure of the outer atmospheric layers as one moves to later spectral types in the Hertzsprung-Russell diagram: a chromosphere is always present, but the coronal emission diminishes and a cool massive wind steps in. Aims. Where most studies have focussed on short-wavelength observations, this article explores the influence of the chromosphere and the wind on long-wavelength photometric measurements. The goal of this study is to assess wether a set of standard near-infrared calibration sources are fiducial calibrators in the far-infrared, beyond 50 mu m. Methods. The observational spectral energy distributions were compared with the theoretical model predictions for a sample of nine K- and M-giants. The discrepancies found are explained using basic models for flux emission originating in a chromosphere or an ionised wind. Results. For seven out of nine sample stars, a clear flux excess is detected at (sub)millimetre and/or centimetre wavelengths, while only observational upper limits are obtained for the other two. The precise start of the excess depends upon the star under consideration. For six sources the flux excess starts beyond 210 mu m and they can be considered as fiducial calibrators for Herschel/PACS (60-210 mu m). Out of this sample, four sources show no flux excess in the Herschel/SPIRE wavelength range (200-670 mu m) and are good calibration sources for this instrument as well. The flux at wavelengths shorter than similar to 1 mm is most likely dominated by an optically thick chromosphere, where an optically thick ionised wind is the main flux contributor at longer wavelengths. Conclusions. Although the optical to mid-infrared spectrum of the studied K- and M-type infrared standard stars is represented well by a radiative equilibrium atmospheric model, a chromosphere and/or ionised stellar wind at higher altitudes dominates the spectrum in the (sub)millimetre and centimetre wavelength ranges. The presence of a flux excess has implications on the role of the stars as fiducial spectrophotometric calibrators in these wavelength ranges.
|
|
