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Further observations of Hipparcos red stars and standards for UBV(RI)C photometry
We present homogeneous and standardized UBV(RI)C JHKphotometry for over 100 M stars selected from an earlier paper on thebasis of apparent photometric constancy. L photometry has been obtainedfor stars brighter than about L = 6. Most of the stars have asubstantial number of UBV(RI)C observations and, it is hoped,will prove useful as red supplementary standards. Additionally, we listJHK photometry for nearly 300 Hipparcos red stars not selected asstandards, as well as L photometry for the brightest stars.
| Hipparcos red stars in the HpV_T2 and V I_C systems
For Hipparcos M, S, and C spectral type stars, we provide calibratedinstantaneous (epoch) Cousins V - I color indices using newly derivedHpV_T2 photometry. Three new sets of ground-based Cousins V I data havebeen obtained for more than 170 carbon and red M giants. These datasetsin combination with the published sources of V I photometry served toobtain the calibration curves linking Hipparcos/Tycho Hp-V_T2 with theCousins V - I index. In total, 321 carbon stars and 4464 M- and S-typestars have new V - I indices. The standard error of the mean V - I isabout 0.1 mag or better down to Hp~9 although it deteriorates rapidly atfainter magnitudes. These V - I indices can be used to verify thepublished Hipparcos V - I color indices. Thus, we have identified ahandful of new cases where, instead of the real target, a random fieldstar has been observed. A considerable fraction of the DMSA/C and DMSA/Vsolutions for red stars appear not to be warranted. Most likely suchspurious solutions may originate from usage of a heavily biased color inthe astrometric processing.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997).}\fnmsep\thanks{Table 7 is onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/397/997
| UBV(RI)C photometry of Hipparcos red stars
We present homogeneous and standardized UBV(RI)C photometryfor nearly 550 M stars selected from the Hipparcos satellite data baseusing the following selection criteria: lack of obvious variability (noHipparcos variability flag); δ<+10°(V-I)>1.7 and Vmagnitude fainter than about 7.6. Comparisons are made between thecurrent photometry, other ground-based data sets and Hipparcosphotometry. We use linear discriminant analysis to determine aluminosity segregation criterion for late-type stars, and principalcomponent analysis to study the statistical structure of the colourindices and to calibrate absolute magnitude in terms of (V-I) for thedwarf stars. Various methods are used to determine the mean absolutemagnitude of the giant stars. We find 10 dwarf stars, apparentlypreviously unrecognized (prior to Hipparcos) as being within 25pc,including five within 20pc.
| Mass-losing stars in the South Galactic CAP
Observations are presented for 162 late-type stars in the South GalacticCap (b<-30 deg) which were selected on the basisof their IRAS 25/12-μm flux ratios as high-mass-loss candidates. JHKLphotometry (over 1100 observations) was obtained for all of the stars,BV(RI)_C photometry for 78 of them and optical spectra for 51. 154 ofthese stars are non-Mira M or S stars, of which many, and possibly all,are semi-regular variables. Of the remaining eight IRAS objects, threeare T Tauri stars, three are interacting binaries and two are carbonstars. A few of the M giants and both of the carbon stars havecircumstellar envelopes of the type more normally associated with Miravariables. These include two 1612-MHz OH maser sources. It is suggestedthat such stars may have been Miras in the recent past, but arecurrently out of the instability strip owing to a recently experiencedhelium-shell flash. Alternatively, some of them could be binary stars,but there is as yet no evidence for the second star. The near-infraredcolours of the M giants are compared with those of similar stars in theBulge. They are similar to those of the inner Bulge and unlike thosefound in either the outer Bulge or the globular clusters. The kinematicsand Galactic distribution of the M giants indicate that they areprobably from a mixed population and that they could be associated withMiras with a range of periods. A comparison of the observed colours withthose derived from models indicates a range of metallicity with the bulkof stars slightly more metal-rich than the Sun. It also revealssignificant numbers of stars with colours outside the predicted range,possible due to the effects of circumstellar reddening or toinadequacies in the models. The most metal-rich examples of the M starshave high mass-loss rates for non-Miras (~10^-6 M_solar yr^-1) and thereare far fewer of them outside than inside the solar circle. This may bedue to a metallicity gradient. These stars have a scaleheight of morethan 500 pc. The two carbon stars have unusual colours and detachedshells. One of them, R Scl, is shown to vary with a period of 379dsuperimposed on a possible second period of about 2300d. The othercarbon star, which is more distant and previously unknown, may also havedouble-period variations.
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