Tartalom
Képek
Kép feltöltése
DSS Images Other Images
Kapcsolódó cikkek
Spectroscopic parameters for 451 stars in the HARPS GTO planet search program. Stellar [Fe/H] and the frequency of exo-Neptunes
To understand the formation and evolution of solar-type stars in thesolar neighborhood, we need to measure their stellar parameters to highaccuracy. We present a catalogue of accurate stellar parameters for 451stars that represent the HARPS Guaranteed Time Observations (GTO)“high precision” sample. Spectroscopic stellar parameterswere measured using high signal-to-noise (S/N) spectra acquired with theHARPS spectrograph. The spectroscopic analysis was completed assumingLTE with a grid of Kurucz atmosphere models and the recent ARES code formeasuring line equivalent widths. We show that our results agree wellwith those ones presented in the literature (for stars in common). Wepresent a useful calibration for the effective temperature as a functionof the index color B-V and [Fe/H]. We use our results to study themetallicity-planet correlation, namely for very low mass planets. Theresults presented here suggest that in contrast to their joviancouterparts, neptune-like planets do not form preferentially aroundmetal-rich stars. The ratio of jupiter-to-neptunes is also an increasingfunction of stellar metallicity. These results are discussed in thecontext of the core-accretion model for planet formation.Based on observations collected at La Silla Observatory, ESO, Chile,with the HARPS spectrograph at the 3.6-m telescope (072.C-0488(E)). FullTables 1 and 3 are only available in electronic form at the CDS vianonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/487/373
| Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 pc-The Southern Sample
We are obtaining spectra, spectral types, and basic physical parametersfor the nearly 3600 dwarf and giant stars earlier than M0 in theHipparcos catalog within 40 pc of the Sun. Here we report on resultsfor 1676 stars in the southern hemisphere observed at Cerro TololoInter-American Observatory and Steward Observatory. These resultsinclude new, precise, homogeneous spectral types, basic physicalparameters (including the effective temperature, surface gravity, andmetallicity [M/H]), and measures of the chromospheric activity of ourprogram stars. We include notes on astrophysically interesting stars inthis sample, the metallicity distribution of the solar neighborhood, anda table of solar analogs. We also demonstrate that the bimodal nature ofthe distribution of the chromospheric activity parameterlogR'HK depends strongly on the metallicity, andwe explore the nature of the ``low-metallicity'' chromosphericallyactive K-type dwarfs.
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
| Magnitude, color and spectral type of AQL X-1 in quiescence
Direct I and V-band imaging of Aql X-1 in quiescence and during outburstmaximum shows that the true optical counterpart is the interloperlocated 0.48'' West of the previously known star. We find for the newcounterpart V = 21.6 and V-I = 2.2 in quiescence, when its contributionto the total light was 12% in V and 22% in I. Analysis of thisphotometry and of low-resolution spectra of the sum of both stars, alsotaken during quiescence, shows that the likely spectral types for thepreviously known star and the optical counterpart are late G and late K,respectively, reddened by E(B-V) = 0.5+/-0.1. Based on observationsobtained at the European Southern Observatory, La Silla, Chile
| Optical studies of transient low-mass X-ray binaries in quiescence. I - Centaurus X-4: Orbital period, light curve, spectrum and models for the system
The results of CCD photometry of the Centaurus X-4 soft X-ray transientsource are presented. Analysis of the observations shows that thebrightness of the system in the quiescent state is modulated with aperiod of 15.1 hours. The mean brightness of the system is variablebetween V of about 18.5 and V = 18.35. In April 1986 an active state wasfound where the object was bluer, brighter by about 0.5 mag in V, andvarying rapidly in an erratic fashion, the quiescent light curve havingdisappeared even in the I-band. The amplitude and general shape of thequiescent light curve seem to be independent of the mean brightness. Arather stable minimum appears at phi of about 0.4, but significantvariability is seen in the phi interval from about 0.4 to 0.8.Low-dispersion spectra taken in the quiescent state reveal that the coolcompanion is a dwarf of spectral type close to K7V. A classicalinterpretation of the system involving a Roche lobe-filling K star isdiscussed.
| G. P. Kuiper's spectral classifications of proper-motion stars
Spectral classifications are listed for over 3200 stars, mainly of largeproper motion, observed and classified by Kuiper during the years1937-1944 at the Yerkes and McDonald Observatories. While Kuiper himselfpublished many of his types, and while improved classifications are nowavailable for many of these stars, much of value remains. For many ofthe objects, no other spectral data exist.
| Dwarf K and M stars in the southern hemisphere.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972AJ.....77..486U&db_key=AST
|
Új cikk hozzáadása
Kapcsolódó hivatkozások
- - (nincs kapcsolódó hivatkozás) -
Új link hozzáadása
Besorolás csoportokba:
|
Pozíciós és asztrometriai adatok
| Csillagkép: | Légszivattyú |
| Rektaszcenzió: | 10h04m33.97s |
| Deklináció: | -39°19'00.8" |
| Vizuális fényesség: | 9.116 |
| Távolság: | 31.017 parszek |
| RA sajátmozgás: | -181.8 |
| Dec sajátmozgás: | 94.2 |
| B-T magnitude: | 10.397 |
| V-T magnitude: | 9.222 |
Katalógusok és elnevezések:
|
