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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.
| Rotational modulation and flares on RS CVn and BY Dra stars. XX. Photometry and spectroscopy of CC Eri in late 1989
The active flaring binary CC Eri was studied via multi-wavelengthobservations involving multi-based photometry and ground- andspace-based spectroscopy. Combining early spectroscopic data with thepresent implies an orbital period of P=1.5615 days. Furthermore, thespectroscopic data suggests spectral types of K7 and M3 for the system.The optical photometry indicated a small spot coverage in late 1989,consistent with data taken a year later which showed CC Eri entering itsbrightest-to-date phase. Two flares were detected in the ultravioletspectral data. These flares radiated 2.7 1031 erg and 1.61031 erg in the C Iv line alone, each with a total estimatedradiative energy budget of ~ 1036 erg. For thehigher-temperature lines, such as C Iv, there was no systematicvariability with phase. The lower-temperature lines show a slightindication of rotational modulation. However, there is a much largerscatter in the individual measurements of the Mg Ii and C Iv fluxes thanwould be expected from measurement errors alone, consistent with anatmosphere showing continual small-scale activity.
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Pozíciós és asztrometriai adatok
| Csillagkép: | Eridánusz |
| Rektaszcenzió: | 02h28m50.49s |
| Deklináció: | -44°06'55.5" |
| Vizuális fényesség: | 8.722 |
| Távolság: | 847.458 parszek |
| RA sajátmozgás: | 4.4 |
| Dec sajátmozgás: | -9.7 |
| B-T magnitude: | 10.853 |
| V-T magnitude: | 8.898 |
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