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Optical spectroscopic and 2MASS measurements of Stephenson Halpha stars
We present the results of spectroscopic observations for 52 objects fromthe list of Halpha emission stars of Stephenson(\cite{Ste86}). Out of six known T Tauri stars observed, five showedHalpha in emission and in one (StHa 40), Halpha changed from being in absorption to emission over a period of two years,accompanied by photometric and spectral type variability. We confirm theT Tauri nature of one Stephenson object (StHa 48) on the basis of thepresence of Halpha and Hbeta in emission, Li Ilambda6708 in absorption, infrared excess and X-ray emission. Among the52 objects observed, there were other emission line objects: 1 Ke star,1 BQ[ ] star, 2 galaxies and 2 Be stars. We present a higher-resolutionspectrum of StHa 62 showing permitted and forbidden lines in emissiontypical of BQ[ ] stars. Twenty five out of 30 newly observed objectsfailed to show Halpha in emission. We also present 2MASSobservations for 112 StHa objects. We suggest three Stephenson objects(StHa 52, 125 and 129) to be YSOs on the basis of 2MASS, IRAS and ROSATobservations. These and all other known YSOs amongst StHa stars arefound in regions of star-forming clouds in Taurus, Orion and Ophiuchus.YSOs at high galactic latitudes in other parts of the sky are thereforerare.Table 2 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/402/963
| 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
| New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| New H-alpha emission stars found above 10 deg galactic latitude
Approximately 1300 5.2 x 5.2 deg red-sensitive objective prism plateshave been searched for H-alpha emission stars in order to complete thesearch of the entire sky. The survey here reported represents 59 percentof the whole sky, defined by the region north of declination -25 deg andmostly further than 10 deg from the Galactic plane; the omitted portionshad already been surveyed, in part at Warner and Swasey, in partelsewhere. Two hundred and six stars have been newly found, mostly ofunknown spectral type. The stars' latitude distribution suggests thatthey are mainly moderately high luminosity disk population stars. Thereare new finds especially in Orion and the Taurus dark clouds (limitingmag of about 13).
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | ג'ירף |
| התרוממות ימנית: | 09h45m00.09s |
| סירוב: | +85°14'40.1" |
| גודל גלוי: | 10.1 |
| תנועה נכונה: | 1.9 |
| תנועה נכונה: | 0.3 |
| B-T magnitude: | 12.391 |
| V-T magnitude: | 10.29 |
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