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מאמרים קשורים
Effective temperature scale and bolometric corrections from 2MASS photometry
We present a method to determine effective temperatures, angularsemi-diameters and bolometric corrections for population I and II FGKtype stars based on V and 2MASS IR photometry. Accurate calibration isaccomplished by using a sample of solar analogues, whose averagetemperature is assumed to be equal to the solar effective temperature of5777 K. By taking into account all possible sources of error we estimateassociated uncertainties to better than 1% in effective temperature andin the range 1.0-2.5% in angular semi-diameter for unreddened stars.Comparison of our new temperatures with other determinations extractedfrom the literature indicates, in general, remarkably good agreement.These results suggest that the effective temperaure scale of FGK starsis currently established with an accuracy better than 0.5%-1%. Theapplication of the method to a sample of 10 999 dwarfs in the Hipparcoscatalogue allows us to define temperature and bolometric correction (Kband) calibrations as a function of (V-K), [m/H] and log g. Bolometriccorrections in the V and K bands as a function of T_eff, [m/H] and log gare also given. We provide effective temperatures, angularsemi-diameters, radii and bolometric corrections in the V and K bandsfor the 10 999 FGK stars in our sample with the correspondinguncertainties.
| 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.
| Photometric Separation of Stellar Properties Using SDSS Filters
Using synthetic photometry of Kurucz model spectra, we explore thecolors of stars as a function of temperature, metallicity, and surfacegravity with Sloan Digital Sky Survey (SDSS) filters, u'g'r'i'z'. Thesynthetic colors show qualitative agreement with the few publishedobservations in these filters. We find that the locus of synthetic starsis basically two-dimensional for 4500 < T < 8000 K, whichprecludes simultaneous color separation of the three basic stellarcharacteristics we consider. Colors including u' contain the mostinformation about normal stellar properties; measurements in this filterare also important for selecting white dwarfs. We identify two differentsubsets of the locus in which the loci separate by either metallicity orsurface gravity. For 0.5 < g' - r' < 0.8 (corresponding roughly toG stars), the locus separates by metallicity; for photometric error of afew percent, we estimate metallicity to within ~0.5 dex in this range.In the range -0.15 < g' - r' < 0.00 (corresponding roughly to Astars), the locus shows separation by surface gravity. In both cases, weshow that it is advantageous to use more than two colors whendetermining stellar properties by color. Strategic observations in SDSSfilters are required to resolve the source of a ~5% discrepancy betweensynthetic colors of Gunn-Stryker stars, Kurucz models, and externaldeterminations of the metallicities and surface gravities. The syntheticstar colors can be used to investigate the properties of any normal starand to construct analytic expressions for the photometric prediction ofstellar properties in special cases.
| On an Adopted Energy Distribution in Stellar Spectra - Main-Sequence Stars of the G-Type
Not Available
| A library of near-IR stellar spectra from 1.328 to 2.5 microns
We present a library of 56 stellar spectra from 1.428 to 2.5 microns,sampling the Hertzsprung-Russell diagram in luminosity class andeffective temperature. Relative fluxes defining the stellar energydistributions throughout the H and K atmospheric windows, an infraredcolor temperature used to set a continuum for equivalent widthmeasurements, and relations between various spectral signatures, colortemperatures and gravity are determined. H2O is the dominant absorber inthe latest M giant stars. Its absorption is measured in both wings ofthe signature around 1.9 micron and a combined effect of H2O and H(-)opacity is measured shortward of 1.6 micron. The CO equivalent widthlongward of 2.29 microns increases with decreasing gravity andtemperature. CO and the OH radical are responsible for numerousabsorption bands below 1.8 micron.
| Association of supernovae with recent star formation regions in late type galaxies
Results are reported from a statistical study carried out to constrainthe various models for the progenitors of supernovae of types Ia, Ib/c,and II. Star-formation regions in late-type galaxies are traced out by HII regions, imaged through photographic and CCD observations, andpossible supernova association with these regions is based on the ratioof the angular separation of each supernova from its nearest H II regionto the angular extent of the H II region in the direction of thesupernova. The specific problems of supernova classification andpositional uncertainties, as well as the probability of chancesuperposition, are also considered. It is suggested that type Iasupernovae do not arise from massive short-lived stellar populations.Type Ib/c and type II supernovae are very likely to be associated with HII regions and therefore with massive stellar progenitors.
| Theoretical colours and isochrones for some Hubble Space Telescope colour systems. II
A grid of synthetic surface brightness magnitudes for 14 bandpasses ofthe Hubble Space Telescope Faint Object Camera is presented, as well asa grid of UBV, uvby, and Faint Object Camera surface brightnessmagnitudes derived from the Gunn-Stryker spectrophotometric atlas. Thesynthetic colors are used to examine the transformations between theground-based Johnson UBV and Stromgren uvby systems and the Faint ObjectCamera UBV and uvby. Two new four-color systems, similar to theStromgren system, are proposed for the determination of abundance,temperature, and surface gravity. The synthetic colors are also used tocalculate color-magnitude isochrones from the list of theoretical tracksprovided by VandenBerg and Bell (1990). It is shown that by using theappropriate filters it is possible to minimize the dependence of thiscolor difference on metallicity. The effects of interstellar reddeningon various Faint Object Camera colors are analyzed as well as theobservational requirements for obtaining data of a given signal-to-noisefor each of the 14 bandpasses.
| Three-color surface photometry of a selected sample of early-type galaxies. I - Observations and data reduction
This paper presents the results of two or three color surface photometryfor a sample of 36 early-type galaxies obtained at the Canada FranceHawaii Telescope with CCD cameras. The calibration and data reductionprocedures are described. A comparison of the results with previous workis made for NGC 3379. For each galaxy the B surface brightness profilealong the major axis, as well as ellipticity and color profiles aredisplayed.
| E. W. Fick Observatory stellar radial velocity measurements. I - 1976-1984
Stellar radial velocity observations made with the large vacuumhigh-dispersion photoelectric radial velocity spectrometer at FickObservatory are reported. This includes nearly 2000 late-type starsobserved during 585 nights. Gradual modifications to this instrumentover its first eight years of operation have reduced the observationalerror for high-quality dip observations to + or - 0.8 km/s.
| Stellar spectrophotometric atlas, wavelengths from 3130 to 10800 A
Over the course of the past 10 years, a large body of homogeneousspectrophotometric data on relatively bright stars has been gathered toserve as a library with which to synthesize galaxy spectra in populationstudies. As the data might be generally useful, they are presented inthree tables. One hundred seventy-five (175) stars were selected, mostfrom the Navy photometric catalog. Covered are complete ranges ofspectral type and luminosity class. Normalized spectral energydistributions of these stars in pictorial form are provided along withtables of calculated colors, scan line and continuum indices, and someinformation on the relation of the scan colors to real photometricsystems.
| Evolutionary synthesis of the stellar population in elliptical galaxies. III - Detailed optical spectra
The evolutionary synthesis technique is used to construct populationmodels for giant elliptical galaxies, using detailed spectrophotometricdata for the galaxies and for stars obtained with the Oke multichannelspectrometer on the Hale telescope. It is found that ellipticals arewell represented by an old, metal-rich population with a turnoff at B-Vof about 0.80 and a turnoff mass function slope of x approximately equalto or less than 1, plus a quite significant contribution from starsabove the turnoff. The nature of these objects is discussed, and it isconcluded that the present data and astrophysical constraints cannotdistinguish between a small young population and a blue stragglerpopulation augmented by a few O stars.
| MK classifications for F-and G-type stars. 3.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974AJ.....79..682H&db_key=AST
| Colors, luminosities, and motions of the nearer G-type stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1964AJ.....69..570E&db_key=AST
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לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | הרקולס |
| התרוממות ימנית: | 16h38m16.18s |
| סירוב: | +29°40'21.0" |
| גודל גלוי: | 7.508 |
| מרחק: | 64.683 פארסק |
| תנועה נכונה: | -34.5 |
| תנועה נכונה: | -191.2 |
| B-T magnitude: | 8.427 |
| V-T magnitude: | 7.584 |
קטלוגים וכינוים:
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INHABITED SKY
