目录
图像
上传图像
DSS Images Other Images
相关文章
Natural Coronagraphic Observations of the Eclipsing T Tauri System KH 15D: Evidence of Accretion and Bipolar Outflow in a Weak-Line T Tauri Star
We present high-resolution (R~44,000) UV-Visual Echelle Spectrographspectra of the eclipsing pre-main-sequence star KH 15D covering thewavelength range 4780-6810 Å obtained at three phases: out ofeclipse, near minimum light, and during egress. The system evidentlyacts as a natural coronagraph, enhancing the contrast relative to thecontinuum of hydrogen and forbidden emission lines during eclipse. Atmaximum light, the Hα equivalent width was ~2 Å and theprofile showed broad wings and a deep central absorption. During egress,the equivalent width was much higher (~70 Å) and the broad wings,which extend to +/-300 km s-1, were prominent. During eclipsetotality, the equivalent width was less than during egress (~40 Å)and the high-velocity wings were much weaker. Hβ showed a somewhatdifferent behavior, revealing only the blueshifted portion of thehigh-velocity component during eclipse and egress. [O I]λλ6300, 6363 lines are easily seen both out of eclipse andwhen the photosphere is obscured and exhibit little or no flux variationwith the eclipse phase. Our interpretation is that KH 15D, althoughclearly a weak-line T Tauri star by the usual criteria, is stillaccreting matter from a circumstellar disk and has a well-collimatedbipolar jet. As the knife-edge of the occulting matter passes across theclose stellar environment, it is evidently revealing structure in themagnetosphere of this pre-main-sequence star with unprecedented spatialresolution. We also show that there is only a small, perhaps marginallysignificant change in the velocity of the K7 star between the maximumlight and egress phases probed here.Based on UV-Visual Echelle Spectrograph observations collected at theEuropean Southern Observatory's Very Large Telescope via Director'sDiscretionary Time, within the observing program P267.C-5736.
| 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
| Large and kinematically unbiased samples of G- and K-type stars. V - Evolved stars in the selected areas at + 15-deg declination
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990PASP..102..242E&db_key=AST
| UBV photometry of stars whose positions are accurately known.
Photometric indices V, B-V, and U-B were measured for about 560 stars ofthe AGK3R and NPZT catalogs between BD declinations 11 deg and 23 deg,using the 40-cm Cassegrain telescope of the Kvistaberg Observatory fromApril 1986 to May 1987. The observation procedure and the reductiontechnique were the same as in the earlier papers of this series by Oja(1984, 1985, 1986, and 1987). The mean errors were calculated from theinternal consistency of the data. The accuracy was found to be the sameas for the earlier parts of the survey.
| A sample of old-disk-population red giants.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976PASP...88..426E&db_key=AST
| Photoelectric radial velocities. IV. 528 7 to 10 mag stars in the +15degree selected areas.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971MNRAS.155....1G&db_key=AST
|
提交文章
相关链接
提交链接
下列团体成员
|
观测天体数据
目录:
|
