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تسجيل مستخدم جديدISOGAL survey of Baades Windows
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The Baades Windows of low obscuration towards the inner parts of the Galactic bulge represent ideal places in which to develop an understanding of the ISOGAL colour-magnitude diagrams. Unlike the case for the solar neighbourhood, their contents are at a uniform distance from the Sun, affected only by the finite thickness of the Bulge. The objects detected in the ISOGAL survey are found to be late-type M-giants at the red giant tip or on the Asymptotic Giant Branch (AGB). The ISOGAL colour-magnitude diagrams show that mass-loss starts at about M4 and increases towards later types. Many non-Miras have mass-loss rates similar to shorter-period Miras. The visible counterparts of the ISOGAL sources have been identified in the database of the MACHO gravitational lensing survey. A first report of this work is included here. It is found that nearly all the ISOGAL sources are semi-regular variables (SRVs), which are many times more numerous than Miras. Their stellar luminosities increase with period. Based on a simple interpretation of the photometry, mass-loss rates from about 10^{-9} to 10^{-7} solar masses per year are found for SRVs with periods in excess of about days.
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In this work, a sample of luminous M-type giants in the Baades Windows towards the inner Galactic Bulge is investigated in the near-infrared. The ISOGAL survey at 7 and 15 micron has given information concerning the mass-loss rates of these stars and
their variability characteristics have been extracted from the MACHO database. Most are known to be semi-regular variables (SRVs). Here we discuss how their IJHK-region colours depend on period and the presence or absence of mass-loss, using results mainly taken from the DENIS and 2MASS surveys. In order to compare their colours with solar neighbourhood stars, photometric colours on the DENIS, 2MASS and ESO photometric systems have been synthesized for objects in the spectrophotometric atlas of Lancon and Wood (2000). In addition, they have been used to predict the differences in colour indicies when stars with strong molecular bands are observed using different photometric systems. The SRVs are found to inhabit the upper end of the J-K, K colour-magnitude diagram, lying just below the Miras. High mass-loss rates are associated with high luminosity. The near-infrared colours of the semi-regular variables increase in a general way with period and are reddest for the stars with significant mass-loss. The average colours of Mira variables, whose periods start at around 200 days in the Bulge, are bluer than those of the semi-regulars at this period, particularly in J-H, thanks to the association of deep water-vapour bands with large amplitude.
By cross-correlating the results of two recent large-scale surveys, the general properties of a well defined sample of semi-regular variable stars have been determined. ISOGAL mid-infrared photometry and MACHO lightcurves are assembled for approximat
ely 300 stars in the Baades Windows of low extinction towards the Galactic bulge. These stars are mainly giants of late M spectral type, evolving along the asymptotic giant branch (AGB). They are found to possess a wide and continuous distribution of pulsation periods and to obey an approximate log~period -- bolometric magnitude relation or set of such relations. Approximate mass-loss rates in the range of 1e-8 to 5e-7 M_sun per year are derived from ISOGAL mid-infrared photometry and models of stellar spectra adjusted for the presence of optically-thin circumstellar silicate dust. Mass-loss rates depend on luminosity and pulsation period. Some stars lose mass as rapidly as short-period Miras but do not show Mira-like amplitudes. A period of 70 days or longer is a necessary but not a sufficient condition for mass loss to occur. For AGB stars in the mass-loss ranges that we observe, the functional dependence of mass-loss rate on temperature and luminosity is found to be in agreement with recent theoretical predictions. If we include our mass-loss rates with a sample of extreme mass-losing AGB stars in the Large Magellanic Cloud, we get the general result for AGB stars that mass-loss rate is proportional to luminosity^{2.7}, valid for AGB stars with 10^{-8} to 10^{-4} M_sun per year (Abridged).
We have searched the OGLE-II archive for candidate counterparts of X-ray sources detected in two low-extinction windows included in our Galactic bulge Chandra/HST survey. We find that a significant number - i.e. in excess of the expected level of ran
dom associations - can be matched with probable M-giants. Their X-ray properties can be understood if these sources are symbiotic binaries where the X-rays are typically, either directly or indirectly, the result of a white dwarf accreting from the wind of a cool giant. Optical and near-infrared properties of selected sources are consistent with a symbiotic nature, although none of the spectra collected for 8 out of 13 candidate counterparts show the high-ionization nebular emission lines observed for many symbiotics. The hard X-ray emission for several sources (power-law photon indices -1.5 ~< Gamma ~< 1.5) suggests our sample includes systems similar to the symbiotics recently detected with INTEGRAL and Swift.
A complete sample of 174 M giants classified by Blanco (1986) and later than subtype M0 in the NGC6522 Baades Window clear field has been investigated to establish some general properties of cool Bulge stars. Photometric information has been obtained
from the MACHO database to search for variability and, where possible, to determine periods. Near- and mid-IR magnitudes have been extracted from DENIS and ISOGAL. 46 semi-regular variables and 2 irregulars were found a mongst the 174. Many M5 and all stars M6 or later show variation, whereas earlier subtypes do not. The DENIS I-J and J-K_S colours and the luminosities of the M stars increase with M sub-class. K tends to increase with log P among M-type SR variables. Almost all the variables were detected at 7 microns during the ISOGAL programme. Excess radiation at 15 microns, indicative of heavy mass loss, is associated with very high luminosity and late spectral type. The limit of sensitivity of the ISOGAL survey was such that the non-variables were not detected. Four probable M stars not listed by Blanco (1986), two of which are semi-regular variables, were detected by ISOGAL. In the case of doubly-periodic SR variables, the longer periods have K mags which place them close to the D line of Wood (2000) in a K,log P diagram. The unusual MACHO light curve of one particular star, Blanco 26, shows the commencement of a long-period variation with an anomalously short and sharp event and appears to rule out a pulsational model for this phenomenon.
We present version 1.0 of the ISOGAL-DENIS Point Source Catalogue (PSC), containing more than 100,000 point sources detected at 7 and/or 15 micron in the ISOGAL survey of the inner Galaxy with the ISOCAM instrument on board the Infrared Space Observa
tory (ISO). These sources are cross-identified, wherever possible, with near-infrared (0.8-2.2 micron) data from the DENIS survey. The overall surface covered by the ISOGAL survey is about 16 square degrees, mostly (95%) distributed near the Galactic plane (|b| < 1 deg), where the source extraction can become confusion limited and perturbed by the high background emission. Therefore, special care has been taken aimed at limiting the photometric error to ~0.2 magnitude down to a sensitivity limit of typically 10 mJy. The present paper gives a complete description of the entries and the information which can be found in this catalogue, as well as a detailed discussion of the data processing and the quality checks which have been completed. The catalogue is available via the VizieR Service at the Centre de Donnees Astronomiques de Strasbourg (CDS, http://vizier.u-strasbg.fr/viz-bin/VizieR/) and also via the server at the Institut dAstrophysique de Paris (http://www-isogal.iap.fr/). A more complete version of this paper, including a detailed description of the data processing, is available in electronic form through the ADS service.
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