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Random forest automated supervised classification of Hipparcos periodic variable stars
We present an evaluation of the performance of an automatedclassification of the Hipparcos periodic variable stars into 26 types.The sub-sample with the most reliable variability types available in theliterature is used to train supervised algorithms to characterize thetype dependencies on a number of attributes. The most useful attributesevaluated with the random forest methodology include, in decreasingorder of importance, the period, the amplitude, the V-I colour index,the absolute magnitude, the residual around the folded light-curvemodel, the magnitude distribution skewness and the amplitude of thesecond harmonic of the Fourier series model relative to that of thefundamental frequency. Random forests and a multi-stage scheme involvingBayesian network and Gaussian mixture methods lead to statisticallyequivalent results. In standard 10-fold cross-validation (CV)experiments, the rate of correct classification is between 90 and 100per cent, depending on the variability type. The main mis-classificationcases, up to a rate of about 10 per cent, arise due to confusion betweenSPB and ACV blue variables and between eclipsing binaries, ellipsoidalvariables and other variability types. Our training set and thepredicted types for the other Hipparcos periodic stars are availableonline.
| AGB variables and the Mira period-luminosity relation
Published data for large-amplitude asymptotic giant branch variables inthe Large Magellanic Cloud (LMC) are re-analysed to establish theconstants for an infrared (K) period-luminosity relation of the formMK = ρ[logP - 2.38] + δ. A slope of ρ = -3.51+/- 0.20 and a zero-point of δ = -7.15 +/- 0.06 are found foroxygen-rich Miras (if a distance modulus of 18.39 +/- 0.05 is used forthe LMC). Assuming this slope is applicable to Galactic Miras we discussthe zero-point for these stars using the revised Hipparcos parallaxestogether with published very long baseline interferometry (VLBI)parallaxes for OH masers and Miras in globular clusters. These result ina mean zero-point of δ = -7.25 +/- 0.07 for O-rich Galactic Miras.The zero-point for Miras in the Galactic bulge is not significantlydifferent from this value.Carbon-rich stars are also discussed and provide results that areconsistent with the above numbers, but with higher uncertainties. Withinthe uncertainties there is no evidence for a significant differencebetween the period-luminosity relation zero-points for systems withdifferent metallicity.
| Reprocessing the Hipparcos data of evolved stars. III. Revised Hipparcos period-luminosity relationship for galactic long-period variable stars
We analyze the K band luminosities of a sample of galactic long-periodvariables using parallaxes measured by the Hipparcos mission. Theparallaxes are in most cases re-computed from the Hipparcos IntermediateAstrometric Data using improved astrometric fits and chromaticitycorrections. The K band magnitudes are taken from the literature andfrom measurements by COBE, and are corrected for interstellar andcircumstellar extinction. The sample contains stars of several spectraltypes: M, S and C, and of several variability classes: Mira, semiregularSRa, and SRb. We find that the distribution of stars in theperiod-luminosity plane is independent of circumstellar chemistry, butthat the different variability types have different P-L distributions.Both the Mira variables and the SRb variables have reasonablywell-defined period-luminosity relationships, but with very differentslopes. The SRa variables are distributed between the two classes,suggesting that they are a mixture of Miras and SRb, rather than aseparate class of stars. New period-luminosity relationships are derivedbased on our revised Hipparcos parallaxes. The Miras show a similarperiod-luminosity relationship to that found for Large Magellanic CloudMiras by Feast et al. (\cite{Feast-1989:a}). The maximum absolute Kmagnitude of the sample is about -8.2 for both Miras and semi-regularstars, only slightly fainter than the expected AGB limit. We show thatthe stars with the longest periods (P>400 d) have high mass lossrates and are almost all Mira variables.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA \cite{Hipparcos}).Table \ref{Tab:data1} is only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/403/993
| 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
| Stars with the Largest Hipparcos Photometric Amplitudes
A list of the 2027 stars that have the largest photometric amplitudes inHipparcos Photometry shows that most variable stars are all Miras. Thepercentage of variable types change as a function of amplitude. Thiscompilation should also be of value to photometrists looking forrelatively unstudied, but large amplitude stars.
| Infrared colours for Mira-like long-period variables found in the (Mȯ<~10-7 Msolar yr-1) Hipparcos Catalogue
Near-infrared, JHKL, photometry is presented for 193 Mira andsemi-regular variables that were observed by Hipparcos; periods,bolometric magnitudes and amplitudes are derived for 92 of them. Becauseof the way in which the Hipparcos targets were selected, this group ofstars provides a useful data base of Miras with low mass-loss rates(Mȯ<~10-7Msolaryr-1).Various period-colour relationships are discussed in detail. The colour,particularly BCK = 10.86 - 38.10 K (J - K)0 +64.16(J - K)20 - 50.72(J -K)30 + 19, K-L, at a given period is found todepend on the pulsation amplitude of the star. A comparison with modelssuggests that this is a consequence of atmospheric extension, in thesense that large-amplitude pulsators have very extended atmospheres andredder Mȯ<10-7Msolaryr-1, K-L and H-K but bluerJ-H than their lower amplitude counterparts. The stars with veryextended atmospheres also have higher values of K-[12] and hence highermass-loss rates. This finding provides further evidence for the causalconnection between pulsation and mass loss. Two sequences are identifiedin the Hp-K versus logP diagram (where Hp is the Hipparcos broad-bandmagnitude) at short periods (logP<2.35). At a given period these twogroups have, on average, the same pulsation amplitude, but differentJHKL colours and spectral types. The short-period stars in the bluersequence have similar near-infrared colours to the Miras found inglobular clusters. Long-term trends in the infrared light curves arediscussed for stars that have sufficient data.
| Coordinates and Identifications for Sonneberg Variables on MVS 272-275
Not Available
| Identification of Variable Stars in the Hubble Space Telescope Guide Star Catalogue
Not Available
| Short- and intermediate-period oxygen-rich Miras
Available IR photometry and the period-IR luminosity relationship areused to analyze a nearly complete sample of oxygen-rich Miras atGalactic latitudes with /b/ greater than 30 deg. In agreement withprevious kinematic studies, a marked difference is found in the spatialdistributions between the stars with periods less than and those withperiods greater than 300 d. For stars with periods in the range 300-400d, the exponential scale height from the Galactic plane is close to 240pc, the projected surface density is about 100/sq kpc, and the localspace density is about 210/cu kpc. The progenitors of the Miras withperiods greater than 300 d appear to be disk dwarfs with typicalmain-sequence masses of between 1.0 and 1.2 solar masses. The masses ofthe main-sequence progenitors of the short-period Miras are 1.1 solarmasses or less. The duration of the Mira phase for theintermediate-period stars is estimated to be about 20,000 yr, somewhatlonger than other recent estimates. Both short- and intermediate-periodoxygen-rich Miras characteristically lose mass at about 10 exp -7 solarmass/yr.
| Revised Elements. II. SV Virginis, BZ Virginis, SW Hydrae, X Arae, BQ Pavonis, and V865 Aquilae
The Mira variables BZ Vir, SW Hya, X Ara, BQ Pav, and V865 Aql,considered for the HIPPARCOS observing program, have been studied usingthe Harvard College Observatory photographic plate collection.Previously published elements have been revised.
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