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מאמרים קשורים
Really Cool Stars and the Star Formation History at the Galactic Center
We present λ/Δλ=550-1200 near-infrared H and Kspectra for a magnitude-limited sample of 79 asymptotic giant branch andcool supergiant stars in the central ~5 pc (diameter) of the Galaxy. Weuse a set of similar spectra obtained for solar neighborhood stars withknown Teff and Mbol that is in the same range asthe Galactic center (GC) sample to derive Teff andMbol for the GC sample. We then construct the H-R diagram forthe GC sample. Using an automated maximum likelihood routine, we derivea coarse star formation history of the GC. We find that (1) roughly 75%of the stars formed in the central few parsecs are older than 5 Gyr; (2)the star formation rate (SFR) is variable over time, with a roughly 4times higher SFR in the last 100 Myr compared to the average SFR; (3)our model can match dynamical limits on the total mass of stars formedonly by limiting the initial mass function to masses above 0.7Msolar (this could be a signature of mass segregation or ofthe bias toward massive star formation from the unique star formationconditions in the GC); (4) blue supergiants account for 12% of the totalsample observed, and the ratio of red to blue supergiants is roughly1.5; and (5) models with isochrones with [Fe/H]=0.0 over all ages fitthe stars in our H-R diagram better than models with lower [Fe/H] in theoldest age bins, consistent with the finding of Ramírez et al.that stars with ages between 10 Myr and 1 Gyr have solar [Fe/H].
| 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
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| Classification and Identification of IRAS Sources with Low-Resolution Spectra
IRAS low-resolution spectra were extracted for 11,224 IRAS sources.These spectra were classified into astrophysical classes, based on thepresence of emission and absorption features and on the shape of thecontinuum. Counterparts of these IRAS sources in existing optical andinfrared catalogs are identified, and their optical spectral types arelisted if they are known. The correlations between thephotospheric/optical and circumstellar/infrared classification arediscussed.
| Luminosity and Temperature from Near-Infrared Spectra of Late-Type Giant Stars
We present moderate resolution (lambda / Delta lambda ~ 1380 and lambda/ Delta lambda ~ 4830) spectra of 43 K0 to M6 III stars covering 2.19 -2.34 mu m and measure equivalent widths of the strongest absorptionfeatures - Na I, Ca I, and (12) CO(2,0) - present on the spectra. Thehigh resolution Wallace & Hinkle (1996) spectral atlas shows thatour moderate resolution measurements of the atomic features havesignificant contributions from other species, such as Sc, S, Fe, Ti, Si,and V. We also find that our measured equivalent widths are affected byCN absorption present in the continuum bands. In spite of this, theequivalent widths of Na I and Ca I features at moderate resolution stillshow a strong dependence on effective temperature. The CO equivalentwidth at moderate resolution is less affected by other lines andcontinuum placement than the atomic features, because of its relativelygreater strength. We compare our data to similar data taken forlate-type dwarf stars (Ali et al. 1995) and find that a two dimensionalspectral classification can be constructed based on the near-IR spectra.The quantity log[EW(CO)/(EW(Na)+EW(Ca))] is a strong luminosityindicator independent of effective temperature, while the equivalentwidth of (12) CO(2,0) has a well-defined dependence on effectivetemperature for a given luminosity. This two dimensional spectralclassification is ideal for cool stars obscured by dust in, for example,the central part of the Galactic bulge and regions of star formation.
| Accurate Positions Of Suspected Variable Stars Near The South Galactic Pole
Not Available
| Asymptotic giant branch stars near the sun
Available red and near-infrared photometry and apparent motions of M, S,and C asymptotic giant branch (AGB) stars in the Bright Star Catalogueare tabulated and discussed. It is shown that the red and near infraredindices normally used for late-type stars are interchangeable except forcarbon stars. The M-type giants are variable with visual amplitudegreater than 0.05 mag. The reddening-free parameter m2 from Genevaphotometry is essentially a temperature parameter for M giants, whilethe reddening-free parameter d is a sensitive detector of blue stellarcompanions. The space density of AGB stars near the sun decreases by afactor of 35 in a temperature range 3800 to 3400 K. Two of the S starsnear the sun were found to have nearly equal space motions and may becomembers of the Arcturus group.
| Narrow-band photometry of late-type stars. II
This paper presents extensive narrow-band photometry in the Uppsalasystem supplementing earlier published mesurements so that data now areavailable for all late-type stars brighter than V = 6.05 and a number ofgalactic cluster members. Numerous UBV and BV measurements are alsopublished. The data are used to determine relations for the predictionof UBV intrinsic colors for late-type stars from the narrow-bandmeasurements. The main purpose of the data is to constitute the basisfor the determination of solar-neighborhood space densities of late-typestars, mainly giants of different kinds; these space densities will becombined with narrow-band data for fainter stars in the north Galacticpole region to yield the decrease of space density with distance fromthe galactic plane for many kinds of late-type stars.
| IRAS catalogues and atlases - Atlas of low-resolution spectra
Plots of all 5425 spectra in the IRAS catalogue of low-resolutionspectra are presented. The catalogue contains the average spectra ofmost IRAS poiont sources with 12 micron flux densities above 10 Jy.
| List of 333 variable, microvariable or suspected variable stars detected in the Geneva photometry
A list is presented of 333 stars, excluded from the GCVS and itssupplements, whose probability of variability ranges from high tocertain. The standard deviations observed in the V magnitude togetherwith the known spectral types, however, only allow speculation as to thetype of variable in question pending supplementary observations whichreveal the individual characteristics of these stars.
| Optical, infrared, and radio studies of AFCRL sources
The southern point sources in the AFCRL infrared (4, 11, and 20 microns)sky survey have been studied at infrared, optical, and radiowavelengths. Searches were performed at 2.2 microns to locate thesources, near-infrared photometry of them was secured, andclassification spectra of those with optical counterparts were obtained.OH observations have yielded 14 new Type II OH/IR sources and suggest acorrelation between the OH flux densities and the infrared colors. Mostof the AFCRL sources are carbon or late M stars similar to the reddestobjects in the IRC but extending to even redder color indices. Inaddition, two emission nebulae are found along with two WC stars, fiveBe stars, and three sources lying in or near reflection nebulae. Theconfirmed sources lie preferentially within a few degrees of thegalactic plane, and the carbon stars show a galactic-longitudedistribution different from that of the remainder. Many of the sourcesprobably vary at infrared wavelengths.
| Spectroscopic observations of M giant stars at the south galactic pole.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1973MNRAS.162...11C&db_key=AST
| The dynamics of M stars in the southern galactic cap.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972ApJ...178..467J&db_key=AST
| Stellar-Population Samples at the Galactic Poles. II. UBVRI Photometry of M Stars Near the South Pole
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970ApJS...22..289E&db_key=AST
| Bright Southern BV-Stars
Not Available
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הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | עגור |
| התרוממות ימנית: | 23h10m09.80s |
| סירוב: | -40°35'30.0" |
| גודל גלוי: | 5.83 |
| מרחק: | 245.098 פארסק |
| תנועה נכונה: | 22.4 |
| תנועה נכונה: | -45.8 |
| B-T magnitude: | 7.967 |
| V-T magnitude: | 6.127 |
קטלוגים וכינוים:
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