THE STANDARD STAR NEWSLETTER

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An electronic publication of the Working Group on Standard Stars

an IAU Interdivisional (IV, V and IX) Working Group

No. 42 Editor: Richard O. Gray
April 2007 grayro@appstate.edu

CONTENTS:

Editorial p. 1
Note from the Working Group Chair, Chris Corbally p. 1
Abstracts of Papers: Blankenberge Standardization meeting p. 2

From the editor

In the previous newsletter, I discussed changes that were made to the website of the Working Group on Standard Stars, in order to make it a better instrument for communicating information on issues relevant to the Standard Stars ``community''. Included in those changes were new webforms for making contributions to this newsletter as well as a link to a web-based discussion forum on Standard Stars. After the publication of that newsletter, a discussion on Vega as the primary standard started, but then flickered and died. Responses to requests for contributions to this newsletter, despite the record-breaking length of newsletter #41, have diminished with time. I would like to solicit from the readers of this newsletter ideas about how the website and this newsletter can be made into a more useful and dynamic tool. Or perhaps the time has come to bid a fond farewell to this newsletter and concentrate on other ways of carrying out the functions of the Working group. What is your opinion?

Richard Gray, editor
grayro@appstate.edu

A Note From the Chair

International Astronomical Union

Working Group on Standard Stars (WGSS)

How well do you remember the time when Commissions and Working Groups were put into the various new IAU Divisions? Well, in the shuffle the Working Group on Standard Stars became designated as a WG of just Commission 45 (Stellar Classification). However the masthead of this Standard Star Newsletter declares that besides Commission 45, Commissions 25 (Stellar Photometry and Polarimetry), 29 (Stellar Spectra), and 30 (Radial Velocities) have an interest in standard star issues. So, with the support of Monique Spite, the Division IV President, I have asked the IAU General Secretary for its status be changed to that of an Inter-Division (IV, V, and IX) working group. The responses from the relevant Divisions and Commissions to regaining the broader scope of the WG have been positive - thank you, if you have been so involved!

Does this really matter? I obviously think so.

My reason is that identifying suitable ``standard stars'' is a broad issue beyond that of the polarimetrists, the radial velocity experts, the flux calibrators, the astrometric people, or the classifiers individually. What is found out about a standard in one regime may well help that standard, or bear on others, in another regime. When a new system, e.g., a photometric one, is developed in one regime or wavelength range, it can impact the use and choice of standards in another. So collaboration is important, and the purpose of this WG on SS is to remind us all of this and to help this happen.

In what might you be helped by collaboration across another regime? Do let us know!

Chris Corbally
corbally@as.arizona.edu

Abstracts

Note: The following abstracts are all from the meeting THE FUTURE OF PHOTOMETRIC, SPECTROPHOTOMETRIC AND POLARIMETRIC STANDARDIZATION, a workshop organised in Blankenberge, Belgium 8-11 May 2006, editor Christiaan Sterken, ASP Conf. Series 2007. In the 41st edition of the Newsletter, we presented abstracts for 46 of the papers presented in that conference. In this newsletter, we present 7 more. This book is now available on the ASP Conference Series website, www.aspbooks.org, although an individual or institutional subscription is required to download the actual papers.

On the Calibration of Multi-object Spectrographs
Nonino, M.; Bono, G.; Monelli, M.; Thevenin, F.; Francois, P.; Buonanno, R.; Corsi, C.E.; Iannicola, G.; Ferraro, I.; Pulone, L.; Moehler, S.; Smith, H.A.; Stetson, P.B.; Walker, A.R.

We present an extensive spectroscopic investigation of evolved old- and intermediate-age stellar tracers of the Carina dSph galaxy. We discuss the approach we devised to calibrate the two European Southern Observatory multi-object spectrographs (FLAMES, FORS2). Pros and cons of the two instruments are also mentioned. Finally, we present preliminary results concerning the radial velocity distribution of the entire star sample ($\sim 1460$ objects).

InfraRed Standards Used for Spectrophotometric Calibration - Application to the Medium Resolution Spectrometer of MIRI
Decin, L.; Bauwens, E.; Blommaert, J.A.D.L.

One of the main ingredients in establishing the relation between input signal and output flux from a spectrometer, is the accurate determination of the spectrophotometric calibration. In case of spectrometers onboard satellites, the accuracy of this part of the calibration pedigree is ultimately linked to the reliability of the candidate calibrators as being fiducial. In this contribution, we deal with the spectrophotometric calibration of infrared spectrometers in the 2 - 200$\mu$m wavelength range. We outline a general selection procedure to arrive at a set of fiducial IR calibrators, and apply the method to the Medium Resolution Spectrometer of MIRI which will be onboard the James Webb Space Telescope.

Standard Stars for Linear Polarization Observed with FORS1
Fossati, L.; Bagnulo, S.; Mason, E.; Landi Degl'Innocenti, E.

We present the analysis of the observations of standard stars for linear polarization obtained from 1999 to 2005 within the context of the calibration plan of the FORS1 instrument of the ESO VLT. We have considered observations carried out both in imaging polarimetric and in spectropolarimetric mode. Broadband polarization was obtained in the Bessel BVRI filters; spectropolarimetry was obtained with various grisms covering different optical ranges and with a typical resolution of a few hundreds. Spectropolarimetric data have been convolved with the transmission functions of the Bessel filters, which enabled us to calculate polarization values equivalent to broadband polarization measurements in imaging mode. Finally, for each star, instrument mode, and for each Bessel filter band, we have calculated an average polarization value obtained after filtering all available data with a $k\sigma$-clipping algorithm.

New Near-infrared Polarimetric Standards
Ageorges, N.

This contribution shows why new standards are needed for near-infrared imaging polarimetry. The meaning of standards for this particular case is explained. Then an ESO project to find new ``calibrators'' is presented and put in perspective with other possibilities.

The Variability of Polarized Standard Stars
Bastien, P.; Vernet, E.; Drissen, L.; Menard, F.; Moffat, A.F.J.; Robert, C.; St-Louis, N.

In the past, different authors have suspected that many linearly polarized standard stars are actually variable objects. This conclusion has been challenged, at least for some of these observations. We revisit this subject and show that while some care is definitely needed, at least some of the stars suspected to vary in fact do vary. Therefore they should no longer be used as polarized standard stars for precision work. A statistical test, better than those used in the past and based on the cumulative distribution function of the polarization data, is presented in some detail.

Using DA White Dwarfs to Calibrate Synthetic Photometry
Holberg, J.B.

Four widely used photometric systems, namely the Johnson-Kron-Cousins UBVRI, the Strömgren uvby, the 2MASS JHKs and the Sloan Digital Sky Survey ugriz systems have been directly compared with the HST absolute photometric scale of Bohlin & Gilliland (2004). These comparisons are subsequently used to construct a large grid of accurate synthetic magnitudes for DA white dwarfs. This grid is, in turn, critically evaluated with respect to the observed photometry from substantial samples of actual white dwarfs. The advantages of DA white dwarfs as photometric stars are emphasized, and the prospects for extending the use of these stars into the near infrared are highlighted.

Standardization: Needs for the Future
Sterken, C.

This paper outlines some of the most stringent needs for the future in the field of standardization in photometry, spectrophotometry and polarimetry.

Contributions to the next Newsletter, due to be ``crystallized'' in October 2007, will be welcomed at any time by the editor (grayro@appstate.edu). Any qualified contribution received will be immediately published on the Standard Star Website, and then appear in the next newsletter. Contributions may be made using the webforms on that website (stellar.phys.appstate.edu/ssn), or may be sent via email to grayro@appstate.edu using the following template.

WHEN SUBMITTING AN ABSTRACT, PLEASE USE THE FOLLOWING TEMPLATE IF POSSIBLE: 

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