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. 43 editor: Richard O. Gray
Oct/Nov 2007 grayro@appstate.edu

CONTENTS:

Editorial p. 1
Note from the Working Group Chair, Chris Corbally p. 1
Contributions: Chris Corbally, Richard Gray, Elizabeth Griffin p. 2
Abstracts of Papers: Margaret Hanson p. 4

From the editor

Apologies to all who went through conniptions waiting for the arrival of this newsletter! But hopefully, the wait will prove to have been worthwhile. This newsletter is distinctly different from the other issues I have edited (and this issue, for better or worse, marks my 7$^{\rm th}$ anniversary as editor) in that its content is dominated by ``contributions'' rather than ``abstracts''. The purpose of this newsletter has always been to stimulate conversation among those who create and use standard stars. I hope that these contributions will stimulate that conversation. Don't wait to contribute your ideas until the call goes out for the next newsletter! Send your contributions to the discussion directly to me at grayro@appstate.edu. They will be published to the website so that the discussion can continue in realtime!

Richard Gray, editor
grayro@appstate.edu

A Note From the Chair

International Astronomical Union

Working Group on Standard Stars (WGSS)

I wonder whether the ``Dipartimento di Fisica dell'Universita degli Studi di Milano'' rings a bell for you? This was actually where this Standard Star Newsletter started since it was the home institute of Prof. Laura E. Pasinetti, the founding editor of the newsletter and first chairperson of the Working Group. On the 14th of last month, the first anniversary of her death, through the efforts of Marco Bersanelli and other colleagues, there was a half-day programme at the Dipartimento to honour Laura. You can find details on the web at

http://www.pubblico.fisica.unimi.it

Those of you who didn't have the pleasure of knowing Laura and of catching her enthusiasm for astronomy might well peruse this website. The presentations and pictures from the commemoration convey what a wonderful person, researcher, and teacher she was, and of course that she had a deep appreciation for the role of standard stars in her work and for maintaining their integrity.

Chris Corbally
corbally@as.arizona.edu

Contributions

Memories of Laura E. Pasinetti

(as read at her first anniversary commemoration, 14 September 2007)

Two things that Laura undertook in 1982 have made me very grateful to her: in August, at the Patras IAU XVIIth General Assembly, she took on the chairmanship for three years of the newly formed working group on standard stars, then sponsored by Commissions 29, 30, and 45; that November she became the founding editor of the ``Standard Stars Newsletter'', continuing in this role until 1990. Now admittedly, managing the new WGSS was not exactly a full-time commitment, and the SSN was not exactly Astronomy & Astrophysics, with some dozen pages appearing twice a year, but Laura's demonstration of willingness to put significant effort into leading this new IAU WG was when I first got to know some important things about her. In her science she had high standards (pun intended) and she wanted to share these, and in personality she was generous and gracious. These characteristics made my subsequent meetings and correspondence with Laura always an occasion to learn and to be of real pleasure.

Laura told me that her first General Assembly, the one when she was appointed an IAU member, was in Prague, so that was in 1967. Since then, her contributions to the work of the IAU through Commissions 4, 29, 45, and 51, and no doubt other branches of which I am unaware, have been steady and definitely helpful. I remember her concern for the archiving and distribution of spectroscopic data, whether photographic or digital, and so, for instance, being actively involved in a European Workshop on the topic at Castel Gandolfo late in 1991. My last contacts with her were while I was president of Commission 45, 2003-2006. Laura would always reply to e-mails that asked for her input, and the wisdom in these replies was clear and welcome.

After the death of her only brother, Laura wrote, ``Each change in our life gives always some pain and sometimes it is difficult to find again the peace.'' Laura would wish that, as we celebrate this high quality scientist, generous teacher and dear friend, we also come to share the lasting peace that she, with her late husband prof. Massimo Fracassini, has now found.

Christopher Corbally, SJ Vice Director, Vatican Observatory

A Standard Field for Surveys?
Richard Gray$^1$
$^1$ Dept. of Physics and Astronomy, Appalachian State University

In the course of an email discussion among the members of the organizing committee of Commission #45, the idea of a Standard Field for Surveys came up. Its genesis was the Joint Discussion sponsored by that commission at the General Assembly in Prague on ``Exploiting Large Surveys for Galactic Astronomy''. The large surveys that were the subject of that JD included SDSS/SEGUE, Gaia, RAVE, 2MASS, Pan-STARRS, LSST, UKIDSS, JASMINE, etc. And surveys continue to proliferate. While the goals of these surveys are all different, (for instance, SDSS focusses primarily on galaxies and quasars, while SDSS/SEGUE and Gaia concentrate on stars and Galactic structure), all of these surveys are obtaining data on stars, and all are using those data to characterize stars in some way. Without exception, these surveys are analyzing those data using automated methods which vary from survey to survey. It occurred to us that it would be very useful for all surveys, as far as it is possible and consistent with their designs, to observe a certain carefully chosen standard field. Such standard field observations would be valuable, as they would allow direct comparisons between the surveys, enabling the detection of systematic differences. Stars in this standard field could also be observed and analyzed with more traditional methods using ground-based telescopes, thus providing a link between tried and true methods, and the constantly evolving new techniques. And while those consistency checks would be of great value, of even greater interest would be the science that would derive from observations of this standard field. The standard field would be the most intensely studied patch of the sky in the history of astronomy, and the stars in that field would be observed in multiple wavelength bands from the X-rays to the far infrared, and we would have precise parallaxes, astrometry and radial velocities for those stars. Multiple observations of the standard field by each survey would give information on variability and binary frequency. A carefully chosen standard field would contain a wide variety of stellar types and stellar populations, and thus those observations would yield important and unique information for the fields of stellar astrophysics and evolution and Galactic structure and evolution.

We are interested in the reactions of the ``standard star community'' to this idea. If it is generally agreed that this is a good idea, it will then be necessary to decide on the size and the location of the field. All ideas and reactions are welcome. Send your thoughts to the editor of the Standard Star Newsletter.

Normal, Abnormal and Standard Stars
Elizabeth Griffin$^1$
$^1$ Dominion Astrophysical Observatory, 5071 West Saanich Road, Victoria, BC, V9E 2E7, Canada

The recent 5-day CP-Ap Vienna Workshop, which brought us well up to date with the most recent modelling and observations of CP-Ap Stars, concentrated on the expected subsets of ``abnormal" late-B and early-A stars that are collectively classified as ``chemically peculiar". The question of normal versus abnormal A-type stars thus reared its head again (as it does at any meeting devoted to these topics), and it may be worth a moment's reflection on what we mean by ``normal" in this context - and whether the use of ``standards" is even meaningful.

Many A-type stars seem to be in a particularly turbulent state of evolution, when seemingly chance combinations of provenance, composition, binarity or magnetism dictate which traditional prototype of Am, Ap, Si-Eu-Cr, solar-like, etc. their surface features resemble. The concept of ``abnormality" thus loses its meaning, since one set of end results is no more likely or unlikely than another. How, then, can ``standards" apply to these sub-categories?

In purely observational terms it matters not which stars are selected as ``standards", provided that we all select the same ones. A standard is merely a reference object, usually chosen for ease of observation. Was the Sun pronounced as a ``standard" because it typifies most early-G objects in our Galaxy? If a standard implies median characteristics, then there should be as many metal-rich stars as there are metal-poor ones with respect to that standard.

Standards in this context can only have scientific relevance as observational calibrators. If we adopt a particular star as a basis for determining absolute quantities such as flux and temperature, i.e. where theory and modelling are invoked or implied, we are likely to incur scaling uncertainties that exceed by an unknown factor the formal errors of fitting to a synthetic spectrum. Using a ``standard" as a calibration of modelled fluxes (as the spectrum of Vega has been used) has no merit beyond demonstrating that one's model happens to fit one's spectrum; it is known that the spectrum of Vega has non-solar characteristics, and the resultant effects in its observed spectrum must be built into any flux-temperature relationship that uses Vega as the flux-calibration standard. Even if one extrapolates that flux-fitting just to other stars of very similar spectral types, those same unspecified limitations to the accuracy do not go away.

The use of standards was exemplified par excellence in the MK classification system, which is purely a description of stellar spectra and was defined by the visual appearance of selected ``standard" ones. The properties of the system and its dependence upon standards are therefore entirely empirical, and the relationship which they bear to ``temperature" is loose (though there have been numerous attempts to quantify it); while spectral type is undoubtedly a conveniently good indicator of that parameter it was not designed as, and consequently cannot be, an exact one. So it is with the A-type stars, where ``peculiar" can just mean ``different". A ``standard" for this purpose is merely a representative of a sub-type, so some standards will be what in another context would be labelled ``abnormal". It would surely be of benefit to identify a formal system of ``Ap standards" as the descriptors of this particular range of stars. And if Richard Gray is right, when he suggests that the ``normal" stars among the A-type stars are actually the Am stars, since ``normal" A-type stars would presumably become Am stars if they did not have ``abnormally" fast rotation, then ``normal" and ``abnormal" in this context lose their meaning altogether.

Abstracts

Near-IR spectral atlas of OB stars (The Astrophysical Journal Supplement Series, Volume 161, Issue 1, pp. 154-170)
Hanson, M. M.$^1$, Kudritzki, R.-P.$^2$, Kenworthy, M. A.$^1$, Puls, J.$^3$ & Tokunaga, A. T.$^2$
$^1$ Department of Physics, The University of Cincinnati
$^2$ Institute for Astronomy, University of Hawai'i
$^3$ Universitäts-Sternwarte München

All spectra published in the above paper have now been placed on the CDS site for direct download. The entry is listed on the ADS. The data include high resolution and very high signal-to-noise H- and K-band spectra of 37 O and early-B standard stars and 6 early-A dwarf stars. The early-A dwarf star spectra will be of considerable value to those removing telluric lines from sources and so we have obtained these spectra for that purpose (see appendix in the paper).

Contributions to the next Newsletter, due to be ``crystallized'' in March 2008, 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 sent via email to grayro@appstate.edu using the following template.

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