Absolute Calibration of Astronomical Flux Standards

Deustua, Susana E.; Kent, Stephen M.; Smith, J. Allyn

doi:10.1007/978-94-007-5618-2_8

Cited by 7 publications

(5 citation statements)

References 86 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Ideally, a spectrophotometer located above any atmospheric absorption could measure the brightness of any star relative to the one standard candle, as long as dynamic range, linearity of response, and out-of-band stray light were not serious issues. Deustua et al (2013) also review absolute flux calibrations but with a much broader brush that covers the entire electromagnetic spectrum from gamma waves to radio wavelengths. This work goes into greater detail on the restricted range of ultraviolet (UV) to mid-infrared (mid-IR).…”

Section: Introductionmentioning

confidence: 99%

Techniques and Review of Absolute Flux Calibration from the Ultraviolet to the Mid-Infrared

Bohlin¹,

Gordon²,

Tremblay³

2014

Publications of the Astronomical Society of the Pacific

182

176

View full text Add to dashboard Cite

The measurement of precise absolute fluxes for stellar sources has been pursued with increased vigor since the discovery of the dark energy and the realization that its detailed understanding requires accurate spectral energy distributions (SEDs) of redshifted Ia supernovae in the rest frame. The flux distributions of spectrophotometric standard stars were initially derived from the comparison of stars to laboratory sources of known flux but are now mostly based on calculated model atmospheres. For example, pure hydrogen white dwarf (WD) models provide the basis for the HST CALSPEC archive of flux standards. The basic equations for quantitative spectrophotometry and photometry are explained in detail. Several historical lab based flux calibrations are reviewed; and the SEDs of stars in the major on-line astronomical databases are compared to the CALSPEC reference standard spectrophotometry. There is good evidence that relative fluxes from the visible to the near-IR wavelength of ∼2.5 µm are currently accurate to 1% for the primary reference standards; and new comparisons with lab flux standards show promise for improving that precision.

show abstract

Section: Introductionmentioning

confidence: 99%

Techniques and Review of Absolute Flux Calibration from the Ultraviolet to the Mid-Infrared

Bohlin¹,

Gordon²,

Tremblay³

2014

Publications of the Astronomical Society of the Pacific

182

176

View full text Add to dashboard Cite

show abstract

“…(s1) Dehaes et al (2011) (s2) Jofré et al (2015) (s3) Baines et al (2010) (s4) Tsuji (1981) (s5) Cohen et al (1999) rect method, like comparison against a blackbody source, or by a indirect method, for example stellar or planetary atmosphere models. Deustua et al (2013) give a detailed description of absolute calibration of astronomical flux standards. Primary flux standards in the far-infrared wavelength range are, with decreasing brightness, planets (Müller et al 2016), asteroids , and stars (Dehaes et al 2011), which are all calibrated via the indirect method and verified by independently calibrated multi-wavelength flux measurements.…”

Section: Namementioning

confidence: 99%

Herschel-PACS photometry of faint stars for sensitivity performance assessment and establishment of faint FIR primary photometric standards

Klaas

Balog

Nielbock

et al. 2018

A&A

View full text Add to dashboard Cite

Aims. Our aims are to determine flux densities and their photometric accuracy for a set of seventeen stars that range in flux from intermediately bright ( 2.5 Jy) to faint ( 5 mJy) 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. Methods. 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.Results. For 15 stars we obtain reliable photometry in at least one PACS filter, and for 11 stars we achieve this in all three PACS filters (70, 100, 160 µm). Faintest fluxes, for which the photometry still has good quality, are about 10 -20 mJy with scan map photometry. The photometry of seven stars is consistent with models or flux predictions for pure photospheric emission, making them good primary standard candidates. Two stars exhibit source-intrinsic far-infrared excess: β Gem (Pollux), being the host star of a confirmed Jupiter-size exoplanet, due to emission of an associated dust disk, and η Dra due to dust emission in a binary system with a K1 dwarf. The investigation of the 160 µm sky background and environment of four sources reveals significant sky confusion prohibiting the determination of an accurate stellar flux at this wavelength. As a good model approximation, for nine stars we obtain scaling factors of the continuum flux models of four PACS fiducial standards with the same or quite similar spectral type. We can verify a linear dependence of signal-to-noise ratio (S/N) with flux and with square root of time over significant ranges. At 160 µm the latter relation is, however, affected by confusion noise. Conclusions. The PACS faint star sample has allowed a comprehensive sensitivity assessment of the PACS photometer. Accurate photometry allows us to establish a set of five FIR primary standard candidates, namely α Ari, ε Lep, ω Cap, HD 41047 and 42 Dra, which are 2 -20 times fainter than the faintest PACS fiducial standard (γ Dra) with absolute accuracy of <6%. For three of these primary standard candidates, essential stellar parameters are known, meaning that a dedicated flux model code may be run.

show abstract

“…[2]), due in large part to atmospheric effects. Hence, accurate measurements made above the atmosphere should reduce the uncertainties A more detailed discussion of the history of Vega's and Sirius' flux calibration can be found in [3]. The HST set of standard stars, observed by every HST instrument to determine zeropoints, derives its photometric absolute flux calibration from white dwarf (WD) models normalized to the 1995 Megessier determination of Vega's flux at 5556 Å. Photometry at wavelengths in the IR, are calculated from zeropoints obtained by extrapolating the WD models to the longer wavelengths.…”

Section: Introductionmentioning

confidence: 99%

HST/WFC3 flux calibration ladder: Vega

et al. 2014

View full text Add to dashboard Cite

Vega is one of only a few stars calibrated against an SI-traceable blackbody, and is the historical flux standard. Photometric zeropoints of the Hubble Space Telescope's instruments rely on Vega, through the transfer of its calibration via stellar atmosphere models to the suite of standard stars. HST's recently implemented scan mode has enabled us to develop a path to an absolute SI traceable calibration for HST IR observations. To fill in the crucial gap between 0.9 and 1.7 micron in the absolute calibration, we acquired -1st order spectra of Vega with the two WFC3 infrared grisms. At the same time, we have improved the calibration of the -1st orders of both WFC3 IR grisms, as well as extended the dynamic range of WFC3 science observations by a factor of 10000. We describe our progress to date on the WFC3 'flux calibration ladder' project to provide currently needed accurate zeropoint measurements in the IR

show abstract

Absolute Calibration of Astronomical Flux Standards

Cited by 7 publications

References 86 publications

Techniques and Review of Absolute Flux Calibration from the Ultraviolet to the Mid-Infrared

Techniques and Review of Absolute Flux Calibration from the Ultraviolet to the Mid-Infrared

Herschel-PACS photometry of faint stars for sensitivity performance assessment and establishment of faint FIR primary photometric standards

HST/WFC3 flux calibration ladder: Vega

Contact Info

Product

Resources

About