STANDARD STAR NEWSLETTER No 39 CONTENTS: Editorial p. 1 Note from the Working Group Chair, Chris Corbally p. 1 Notes and Abstracts: Stritzinger et al., Kazlauskas et al. p. 2 Contributions: H{\o}g et al. ``GAIA Photometric Systems'' p. 3 Meetings: IAU Symposium 240 ``Binaries'', JD 13 ``Surveys'', Standardization Meeting p. 9 From the editor Standard Star Newsletter \#31 included a number of entries about the GAIA spacecraft, and you will see that in this issue, GAIA also features very prominently. We now know the photometric system (actually systems) which will be used on the GAIA spacecraft, due to be launched in 2011 by ESA. Since these systems will play a major role in the lives of those of us who deal with stellar photometry (and will not be retired by the time the data are released!), I am pleased to publish, in this newsletter, a definitive article on these photometric systems. A Note From the Chair International Astronomical Union} Working Group on Standard Stars (WGSS) If you have not done so already, then you will soon notice that the IAU is gearing up for the General Assembly next August, 2006, in Prague. I am looking forward to this GA, and not just because people tell me that Prague is a wonderful city to visit. Yes, the GA is a great forum in which to meet one's friends and colleagues, besides providing all the scientific content that will be on offer. The GA is also a time for Commissions and Working Groups to take stock. There is nothing that says the Working Group on Standard Stars should be permanent, even while astronomers must continue to work on standards. Somehow, though, there must be co-ordination of standards, else there will be chaos within our fields of astrometry, photometry, radial velocities, and spectroscopy. So what ``standards", and in what field, do you think are most in need of co-ordination right now? What might be the way to achieve that co-ordination? Is this best done ``around the table" like the recent unification of the T-dwarf standards, or should sometimes a wider meeting be organized? What is the role of the IAU, facilitator or just promulgator, in such co-ordination? Hearing your reflections on these questions is just another reason why I am looking forward to the IAU-GA in Prague. But do feel free to start the dialogue beforehand by contacting me directly or by writing a reaction for the next SS Newsletter. Chris Corbally corbally@as.arizona.edu Abstracts An Atlas of Spectrophotometric Landolt Standard Stars M. Stritzinger$^1$, N. Suntzeff$^2$, M. Hamuy$^3$, P. Challis$^4$, R. Demarco$^5$, L. Germany$^6$, and A. Soderberg$^7$ $^1$ Max Planck Institute f\"ur Astrophysik $^2$ Cerro Tololo Inter-American Observatory $^3$ Las Campanas Observatory $^4$ Harvard-Smithsonian Center for Astrophysics $^5$ Department of Physics and Astronomy, Johns Hopkins University $^6$ European Southern Observatory $^7$ Caltech Institute of Technology We present CCD observations of 102 Landolt standard stars obtained with the R-C spectrograph on the CTIO 1.5 m telescope. Using stellar atmosphere models we have extended the flux points to our six spectrophotometric secondary standards, in both the blue and the red, allowing us to produce flux-calibrated spectra that span a wavelength range from 3050~\AA\ to 1.1 $\mu$m. Mean differences between $UBVRI$ spectrophotometry computed using Bessell's standard passbands and Landolt's published photometry is found to be 1$\%$ or less. Observers in both hemispheres will find these spectra useful for flux-calibrating spectra and through the use of accurately constructed instrumental passbands be able to compute accurate corrections to bring instrumental magnitudes to any desired standard photometric system (S-corrections). In addition, by combining empirical and modeled spectra of the Sun, Sirius and Vega, we calculate and compare synthetic photometry to observed photometry taken from the literature for these three stars. Published in PASP 117, 810 For reprints, contact M. Stritzinger stritzin@mpa-garching.mpg.de Photoelectric photometry of 800 stars in the Vilnius and Stromgren systems A. Kazlauskas$^1$, R.P. Boyle$^2$, A.G. Davis Philip$^3$, V. Straizys$^1$, V. Laugalys$^1$, K. \v{C}ernis$^1$, S. Bartasiute$^{1,4}$ and J. Sperauskas$^{1,4}$ $^1$ Institute of Theoretical Physics and Astronomy, Vilnius University, Gostauto 12, Vilnius LT-01108, Lithuania $^2$ Vatican Observatory Research Group, Steward Observatory, Tucson, AZ 85721, U.S.A. $^3$ Union College and Institute for Space Observations, Schenectady, NY 12308, U.S.A. $^4$ Astronomical Observatory of Vilnius University, Ciurlionio 29, Vilnius LT-03100, Lithuania The results of new photoelectric photometry of about 800 stars of various spectral types in the Vilnius and Str\"omgren photometric systems are given. The lists include stars with known effective temperatures, gravities (or luminosities) and metallicities which will be used for a new calibration of color indices of the Vilnius and Str\"omvil systems in physical parameters of stars. The observations were obtained in 2000--2004 on the 150 cm telescope of the University of Arizona on Mt. Lemmon. Accepted by BALTIC ASTRONOMY, VOL. 14, NO. 4, 2005 For preprints, contact straizys@itpa.lt Contributions The Multicolor Photometric Systems for GAIA E. Hog$^1$, C. Jordi$^2$ and V. Straizys$^3$ $^1$ Copenhagen University Observatory, Juliane Maries Vej 30, DK-2100, Copenhagen {\O}, Denmark $^2$ Department of Astronomy and Meteorology, Barcelona University, Avda. Diagonal 647, E-08028 Barcelona, Spain $^3$ Institute of Theoretical Physics and Astronomy, Vilnius University, Gostauto 12, Vilnius LT-01108, Lithuania INTRODUCTION The Gaia space mission of ESA will consist of a spacecraft measuring precise coordinates, proper motions, parallaxes, radial velocities and multicolor magnitudes of stars and other objects. Here we shall describe the photometric capabilities of Gaia according to the current design resulting from a technological assessment phase ending mid-2005. The design presently being undertaken by industry may differ in details from the present description but the performance will remain. The Gaia spacecraft is scheduled for launch in 2011. It contains two telescopes called Astro and Spectro. Astrometric and five-color broad-band photometric measurements will be carried out with the Astro telescope which has two entrance mirrors with apertures of 1.4$\times$0.5~m$^2$ from which the light is focussed onto one focal plane. Medium-band 14-color photometric observations and spectral measurements of radial velocities will be carried out with the Spectro telescope with an aperture of 0.5$\times$0.5~m$^2$. The final catalogue should contain about 1 billion stars down to 20th magnitude. For the photometric classification of stars and other purposes, two photometric systems will be implemented. The choice of the optimum passbands for both Gaia systems was finished in December of 2004, resulting from years of intensive work in the Gaia Photometry Working Group. One of the systems is a 5-color broad-band system (designated C1B) and the other is a 14-color medium-band system (designated C1M). The main purpose of both systems is multidimensional classification of faint stars. In the medium-band system for early-type stars the limiting magnitude is expected to be about 18th mag, while in the broad-band system the stars down to 20th mag will be accessible. Naturally, the classification possibilities of the broad-band system are more limited. However, when the measurements of stars in both systems are available, their color indices may be combined in the classification process. Since the Spectro telescope has a lower angular resolution than the Astro telescope, the broad-band system (without the ultraviolet magnitude) is the only tool for classification of stars in crowded fields. Additionally, for a majority of stars trigonometric parallaxes will be available, and this gives additional possibilities in the determination of physical parameters of stars. The selection of optimum passbands of both systems for Gaia was based on synthetic spectra of model stellar atmospheres. The comparison of classification qualities of various systems was done using the so-called ``figure-of-merit" developed by L. Lindegren and based on the recognition of physical properties of the ``scientific targets" -- the stars representing the main Galactic populations. The systems were also tested by a ``blind classification" method. The testing methods used are described in a number of papers available in the Internet site of the Gaia Photometric Working Group (www.am.ub.es/PWG/). In many cases the experience gained up to now by applying the existing ground-based photometric systems (UBVRI, Geneva, Stromgren, Vilnius, Stromvil) and their classification methods were taken into account. THE BROAD-BAND PHOTOMETRIC SYSTEM For the classification of stars a broad passband in the near ultraviolet between 300 and 380 nm is most important. The color index formed from the ultraviolet and blue magnitudes gives the height of the Balmer jump which is the feature in the spectra of B--A--F stars most sensitive to the temperature and gravity. All the ground-based broad and medium band systems use an ultraviolet passband. Classical examples are the broad-band UBV and Sloan photometric systems. Since CCDs in the Astro focal plane are not sensitive to the ultraviolet, and the telescope contains silver-coated mirrors, there is no possibility to use the broad-band photometer to measure ultraviolet radiation. However, a broad ultraviolet passband has been implemented in the Spectro photometer, and this makes it possible to use the ultraviolet magnitudes together with other broad passbands of the Astro photometer. Transmittance curves of the interference filters versus wavelength are of symmetrical trapezoidal shape. The passbands are chosen to satisfy both the astrophysical needs and the specific requirements for chromaticity calibration of the astrometric instrument. The final C1B system contains the five passbands shown in Figure 1. The filters of the system are designated as C1Bxxx, where xxx is the mean wavelength in nanometers. Hereafter filter names will be used without C1, for briefness. The main parameters of the C1B system are listed in Table 1. The response of the shortest filter, B431, (after convolution with the sensitivity of CCD) is quite similar to that of the $B$ passband of the UBV system. The mean wavelengths of both passbands are: 445 nm for B431 and 442 nm for $B$. The mean wavelength and half-width of the B556 response function is very similar to that of the $V$ passband of the UBV system. As a result, color index B431 -- B556 is easily transformable to Johnson's B-V and vice versa. This will facilitate a comparison of the numerous ground-based investigations in the BV system with the Gaia results. In the absence of the ultraviolet color, the differences of ``blue minus green" or ``blue minus red" magnitudes may serve as a measure of metallic-line blanketing, of course much less sensitive than a color index containing ultraviolet. The calculation of synthetic color indices by convolving energy distribution curves of stars with the Gaia C1B system response curves shows that in the B431 -- B556 vs. B556 -- B768 diagram the deviations of F--G metal-deficient dwarfs and G--K metal-deficient giants from the corresponding sequences of solar metallicity are up to 0.07 and 0.20 mag, respectively, i.e., the metallicity effect is easily measurable. The mean wavelength of the B655 filter is close to the position of the narrow-band filter M656 in the Gaia medium-band system. Fluxes Table 1. Filters of the Gaia broad-band photometric system C1B. Passband & C1B431 & C1B556 & C1B655 & C1B768 & C1B916 lambda_0 (nm) & 431 & 556 & 655 & 768 & 916 Delta lambda (nm) & 102 & 128 & 70 & 156 & 100 fig1 Response curves of the C1B broad-band system. The transmittance of the filters is folded with the transmittance of optics and QE of CCDs. The spectral energy distributions of A0 V, G2 V and K7 V type stars in units of W m$^{-2}$ Hz$^{-1}$ are overplotted as reference (the vertical scale factor is arbitrary). measured in both these filters may be combined to form the index measuring the strength of the H$\alpha$ line, almost independent of the interstellar reddening. The strength of absorption in H$\alpha$ line is sensitive to the temperature and luminosity in early-type stars. The same reddening-free index will be used for the identification of emission-line stars. The two remaining red and infrared passbands, B768 and B916 give the height of the Paschen jump which is a function of the temperature and gravity. However, the maximum height of the Paschen jump is 0.3 mag only, i.e., it is about four times smaller than the Balmer jump. To measure its height, the B768 -- B916 must be measured with higher accuracy. Color indices B556 -- {\it B768 and B556 -- B916 for unreddened late-type stars may be used as criteria of the temperature. These color indices (and B768 -- B916) may be used also for separation of cool oxygen-rich (M) and carbon-rich (N) stars. The M326 -- B431 vs. B431 -- B556 diagram shares all the properties of the U-B vs. B-V diagram of Johnson's system and of similar diagrams of other systems. Supergiants are well separated from the main-sequence stars. Metal deficient F--G dwarfs and G--K giants exhibit ultraviolet excesses up to 0.4 mag, blue horizontal branch stars show ultraviolet deficiencies up to 0.3 mag, while white dwarfs are situated around the interstellar reddening line of O-type stars. THE MEDIUM-BAND PHOTOMETRIC SYSTEM The medium-band photometric system C1M has the aim to classify the observed objects (stars, quasars, galaxies, solar system bodies, etc.) and to determine astrophysical parameters of stars (i.e., effective temperature $T_eff, gravity log g or luminosity M_V, metallicity [M/H], the ratio of oxygen and carbon abundances, peculiarity type, the presence of emission, etc.) in the presence of different and unknown interstellar reddening, without any preliminary information. Later on it was decided to add one more parameter, the ratio of abundances of $\alpha$-process elements to iron. The task was complicated by the absence of synthetic spectra of some types of stars, such as carbon and barium stars, Be-stars, Ap and Am stars, etc. An additional problem was the estimation of the possible influence of variations in the interstellar extinction law. The selected system consists of 14 passbands. Their parameters are listed in Table 2 and the transmittance curves of the corresponding filters are shown in Figure 2. The filter at the shortest wavelengths is M326 with a half-width of 82 nm. Thus, this passband actually belongs to a broad-band type, and it may be used to supplement the Gaia broad-band system C1B described earlier. Color indices M326 -- B431 or M326 -- M410 give the height of the Balmer jump, which is a function of $T_{\rm eff$ and $\log g$ in B--A--F stars. In F--G--K stars these color indices measure metallic-line blanketing in the ultraviolet which can be calibrated in [Fe/H] abundances. The mean wavelength of this passband, calculated convolving the filter transmittance, the quantum efficiency of the CCD chip and the reflectance from 4 aluminized mirrors, is 330.5 nm. The M379 passband in early-type stars is placed on the crowding of high member lines of the Balmer series. The absorption in these lines is very sensitive to log g (or M_V). In late-type stars the position of this passband coincides with strong blocking of the spectrum by metallic lines. Thus, the color index M379 -- M467 is a sensitive criterion of metallicity. Analogues in other photometric systems are: the $P$ passband in the Vilnius system and the $L$ passband in the Walraven system. The violet M410 passband measures the spectrum intensity redwards from the Balmer jump. In combination with M326 it gives the height of the jump. For K--M stars it is the shortest passband which, being combined with longer passbands, may give temperatures and luminosities of solar metallicity stars in the presence of interstellar reddening (i.e., in the case when the stars are too faint to be measured in the ultraviolet). Its analogues are: v in the Str\"omgren system, B_1 in the Geneva system and X in the Vilnius system. The blue M467 passband measures the pseudocontinuum in stellar spectra since in this spectral region metallic lines are less numerous than on both sides. Color Table 2. Filters of the Gaia medium-band photometric system C1M. Passband & C1M326 & C1M379 & C1M395 & C1M410 & C1M467 & C1M506 & C1M515 lambda0 (nm) & 326 & 379 & 395 & 410 & 468 & 506 & 515 Delta lambda & 82 & 24 & 10 & 20 & 20 & 36 & 18 Passband & C1M549 & C1M656 & C1M716 & C1M747 & C1M825 & C1M861 & C1M965 lambda0 (nm) & 549 & 656.3 & 717 & 747 & 825 & 861 & 965 Delta lambda & 22 & 7 & 26 & 32 & 34 & 32 & 70 fig2 Response curves of the C1M medium-band system. The transmittance of the filters is folded with the transmittance of optics and QE of CCDs. The spectral energy distributions of A0V, G2V and K7V type stars in units of W m$^{-2}$ Hz$^{-1}$ are overplotted as reference (the vertical scale factor is arbitrary. indices M467 -- M549 or M467 -- M716 may be used as criteria of the temperature for stars of all spectral classes except M and N stars. The analogues of M467 are: b in the Stromgren system, B_2 in the Geneva system, Y in the Vilnius system. The analogues of M549 are: y in the Stromgren system and V in the Vilnius system. The green M515 passband is placed on a broad spectral depression seen in the spectra of G and K stars and formed by crowding of numerous metallic lines. Among them, the strongest features are the Mg I triplet and the MgH band. The depth of this depression is very sensitive to gravity, being deeper in dwarfs than in giants. The same passband is also a useful criterion for identification of Ap stars of the Sr-Cr-Eu type (as in the Maitzen system). The same passband (Z) is also used in the Vilnius system. It is believed that the magnitude difference M506 -- M515 will be sensitive to the Mg/Fe abundance ratio, here M506 is another passband from the Gaia list, being much broader and including the M515 band region. Consequently, this difference may be a criterion of the $\alpha$-process element abundance. Another passband for the same purpose is M395 which measures the intensity of Ca\,II H+K lines. The narrow passband M656 is placed on the H$\alpha$ line. As it was mentioned earlier, the difference of magnitudes B655 -- M656 will be a measure of the intensity of the H$\alpha$ line, most useful for identification of emission-line stars (Be, Oe, Of, T Tau, Herbig Ae/Be, etc.). The deep red M716 passband for stars earlier than M0 may be used as a continuum point. In the spectra of M-type stars it coincides with one of the deepest TiO absorption bands with the head at 713 nm. The next passband M747 coincides with a peak between two TiO bands, so the index M716 -- M747 is a strong indicator of the presence and intensity of TiO. This makes it possible to recognize M-type stars. The last three infrared passbands also serve some different tasks. First, the M861 passband is included in order to serve as the sky mapper for the radial-velocity spectrometer. Second, the color index M825 -- M965 measures the height of the Paschen jump, and the index M861 -- M965 measures the gravity-sensitive absorption of the high member lines of the Paschen series. And third, the index M825 -- M861 is a sensitive criterion for separation of M-type (oxygen-rich) and N-type (carbon-rich) stars, since at 825 nm there is an intensity peak between two TiO bands in M stars and a group of strong CN bands in carbon stars. CONCLUSIONS In the magnitude range, where both broad-band and medium-band photometric measurements will be available, the following stellar parameters will be obtained: Teff, log g (or M_V) and interstellar extinction A_V for all spectral classes (from O to M). In addition, for F--G--K spectral classes, the metallicity parameter [M/H] and (maybe) the ratio of $\alpha$-process element abundance to iron abundance, will be determined. We also have a possibility to identify chemically peculiar stars of types Am, Fm, Ap, Bp, carbon-rich stars (R, N, Ba, CH), emission-line stars (Oe, Of, WR, Be, Herbig Ae/Be, T Tau-type, etc.) and white dwarfs. There will be a possibility to recognize many types of unresolved binaries and to classify their components by modeling their color indices. If the limiting magnitude for the medium-band system is 18, the expected number of stars with three-dimensional (Teff, log g, [M/H]) classification and accurate distances will be of the order of 250$\times$10$^6$. For the stars where only broad-band measurements will be available, the classification possibilities are much lower. In this case the degeneracy of color indices will be great, especially in the presence of interstellar reddening. We expect some positive results will be possible at higher Galactic latitudes where interstellar reddening is either close to zero or can be taken into account by some dust distribution model in the Galaxy. Additional information on distances and absolute magnitudes will be given by trigonometric parallaxes. Meetings IAU Symposium 240, ``Binary Stars as Critical Tools & Tests in Contemporary Astrophysics" Dates: 22-25 August 2006 Location: Prague, Czech Republic Program: This symposium will be held during the 26th General Assembly of the IAU in Prague, Czech Republic. We believe this is the first major meeting in recent memory bringing together members of both the ``wide" and ``close" binary communities. Topics to be included range from common proper motion pairs and other ``fragile" binaries to contact binaries and star/brown-dwarf and star/planet systems, from long-baseline interferometry to theories of binary formation. Our goal is to have a meeting which will appeal to all binary and multiple star researchers. Contact email: William I. Hartkopf wih@usno.navy.mil See http://ad.usno.navy.mil/iaus240/ for more information. Joint Discussion 13, ``Exploiting Large Surveys for Galactic Astronomy'' Dates: 22--23 August 2006 Location: Prague, Czech Republic Program: This joint discussion is taking place during the 26th General Assembly of the IAU in Prague, Czech Republic. The scientific program topics to be covered include: 1) A review of major surveys: photometric, spectroscopic, radial velocity, astrometric, variable star, 2) Impact of these data on models for the formation and evolution of the Galaxy and its substructures, 3) Limitations of surveys: photometric accuracy, spectroscopic discrimination, calibration, parameterization, population synthesis, and 4) Future strategies for space- and ground-based surveys. Contact email: Coryn Bailer Jones calj@mpia.de, Chris Corbally corbally@as.arizona.edu, Sunetra Giridhar giridhar@iiap.res.in See http://clavius.as.arizona.edu/vo/jd13/ for more information CONFERENCE ANNOUNCEMENT C. Sterken$^1$ $^1$ University of Brussels \\ THE FUTURE OF PHOTOMETRIC, SPECTROPHOTOMETRIC AND POLARIMETRIC STANDARDIZATION Every aspect of calibrated measurement of starlight has changed since the last great discussions of standardization problems in Rome and in Dublin in the 1950s. The astronomical community worldwide urgently needs the best possible standardization procedures for modern detectors, large telescopes, all-sky surveys, and the new generation of telescopes orbiting the earth. It is a matter of highest priority to provide a broad and deep overview of all aspects and problems of standardization in these measurement techniques. The aim of the meeting is to convene some renowned experts of standardisation to provide a comprehensive overview and documentation on the state of these techniques, and to elaborate a roadmap to guide the young generation towards consistent calibration of their large databases. Contact csterken@vub.ac.be Preliminary website http://www.vub.ac.be/STER/standards/stds.html Contributions to the next Newsletter, due out in April 2006, will be welcomed at any time by grayro@appstate.edu. WHEN SUBMITTING AN ABSTRACT, PLEASE USE THE FOLLOWING TEMPLATE IF POSSIBLE: \begin{center}{\Large\bf{ Title }}\\{\bf{ A. Author$^1$ and B. Author$^2$ }}\\{\footnotesize $^1$ Institute One and Address \\ $^2$ Institute Two and Address }\end{center} \smallskip{ TEXT OF ABSTRACT }\\{\bf Accepted by} JOURNAL \\{\it For preprints, contact} YOUR ELECTRONIC ADDRESS