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Stellar sources in the ISOGAL intermediate bulge fields
We present a study of ISOGAL sources in the ``intermediate'' galacticbulge (|l|< 2o, |b| ~ 1o-4o),observed by ISOCAM at 7 and 15 mu m. In combination with near-infrared(I, J, Ks) data of DENIS survey, complemented by 2MASS data,we discuss the nature of the ISOGAL sources, their luminosities, theinterstellar extinction and the mass-loss rates. A large fraction of the1464 detected sources at 15 mu m are AGB stars above the RGB tip, anumber of them show an excess in ([7]-[15])0 and(Ks-[15])0 colours, characteristic of mass-loss.The latter, especially (Ks-[15])0, provideestimates of the mass-loss rates and show their distribution in therange 10-8 to 10-5 Msunyr-1.This is paper No. 14 in a refereed journal based on data from the ISOGALproject.Based on observations with ISO, an ESA project with instruments fundedby ESA Member States (especially the PI countries: France, Germany, TheNetherlands and the UK) and with the participation of ISAS and NASA.Based on observations collected at the European Southern Observatory, LaSilla, Chile.
| Mass-losing Semiregular Variable Stars in Baade's Windows
By cross-correlating the results of two recent large-scale surveys, thegeneral properties of a well-defined sample of semiregular variablestars have been determined. ISOGAL mid-infrared photometry (7 and 15μm) and MACHO V and R light curves are assembled for approximately300 stars in the Baade's windows of low extinction toward the Galacticbulge. These stars are mainly giants of late M spectral type, evolvingalong the asymptotic giant branch (AGB). They are found to possess awide and continuous distribution of pulsation periods and to obey anapproximate logP-Mbol relation or set of such relations.Approximate mass-loss rates M in the range of ~1×10-8to 5×10-7 Msolar yr-1 are derivedfrom ISOGAL mid-infrared photometry and models of stellar spectraadjusted for the presence of optically thin circumstellar silicate dust.Mass-loss rates depend on luminosity and pulsation period. Some starslose mass as rapidly as short-period Mira variables but do not showMira-like amplitudes. A period of 70 days or longer is a necessary butnot sufficient condition for mass loss to occur. For AGB stars in themass-loss ranges that we observe, the functional dependence of mass-lossrate on temperature and luminosity can be expressed asM~TαLβ, whereα=-8.80+0.96-0.24 andβ=+1.74+0.16-0.24, in agreement with recenttheoretical predictions. If we include our mass-loss rates with a sampleof extreme mass-losing AGB stars in the Large Magellanic Cloud andignore T as a variable, we get the general result for AGB stars thatM~L2.7, valid for AGB stars with10-8
| ISOGAL survey of Baade's Windows in the mid-infrared
The ISOGAL mid-infrared survey of areas close to the Galactic plane aimsto determine the stellar content of those areas, and its possiblebearing on the history of the Galaxy. The NGC 6522 and Sgr I Baade'sWindows of low obscuration towards the inner parts of the Galactic bulgerepresent ideal places in which to calibrate and understand the ISOGALcolour-magnitude diagrams, which are more difficult to interpret inheavily reddened fields. The survey observations were made with theISOCAM instrument of the ISO satellite. The filter bands chosen were LW2(~7mum) and LW3 (~15mum). The results presented here show that most ofthe detected objects are late M-type giants on the asymptotic giantbranch (AGB), with a cut-off for those earlier than M3-M4. The mostluminous members of these two bulge fields at 7mum are the Miravariables. However, it is evident that they represent the end of asequence of increasing 15-μm dust emission which commences with Mgiants of an earlier sub-type. In observations of late-type M giants,the ISOCAM 15-μm band is mainly sensitive to the cool silicate oraluminate dust shells which overwhelm the photospheric emission.However, in ordinary M-giant stars, the 7-μm band is not stronglyaffected by dust emission and may be influenced instead by absorption.The nu_2 band of water at 6.25mum and the SiO fundamental at 7.9mum arelikely contributors to this effect. Miras are more luminous at 7mum andhave redder K_0-[7] colours than other M giants. Their [7]-[15] coloursare consequently bluer than might be expected by extrapolating fromwarmer M giants. A group of late-M stars has been found that vary littleor not at all, but have infrared colours typical of well-developed dustshells. Their luminosities are similar to those of 200-300 day Miras,but they have slightly redder [7]-[15] colours which form an extensionof the ordinary M-giant sequence. They may belong to the class of redsemi-regular variables. The Mira dust shells show a mid-infrared[7]-[15] colour-period relation. In these two fields there is nocomponent of high-luminosity late-type variables obscured at K andshorter wavelengths such as is seen in the Magellanic Clouds. The upperlimit of long-period variable (LPV) periods in these fields remains atapproximately 700d.
| The Henry Draper Extension Charts: A catalogue of accurate positions, proper motions, magnitudes and spectral types of 86933 stars
The Henry Draper Extension Charts (HDEC), published in the form offinding charts, provide spectral classification for some 87000 starsmostly between 10th and 11th magnitude. This data, being highlyvaluable, as yet was practically unusable for modern computer-basedastronomy. An earlier pilot project (Roeser et al. 1991) demonstrated apossibility to convert this into a star catalogue, using measurements ofcartesian coordinates of stars on the charts and positions of theAstrographic Catalogue (AC) for subsequent identification. We presenthere a final HDEC catalogue comprising accurate positions, propermotions, magnitudes and spectral classes for 86933 stars of the HenryDraper Extension Charts.
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | קשת |
| התרוממות ימנית: | 17h59m16.69s |
| סירוב: | -29°00'11.6" |
| גודל גלוי: | 9.679 |
| תנועה נכונה: | -8.3 |
| תנועה נכונה: | -16.8 |
| B-T magnitude: | 11.248 |
| V-T magnitude: | 9.809 |
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