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The Frequency of Warm Debris Disks and Transition Disks in a Complete Sample of Intermediate-Mass Glimpse Stars: Placing Constraints on Disk Lifetimes
The incidence of dusty debris disks around low- and intermediate-massstars has been investigated numerous times in order to understand theearly stages of planet formation. Most notably, the InfraredAstronomical Satellite (IRAS) mission observed the entire sky at mid-and far-infrared (IR) wavelengths, identifying the first debris disksystems, but was unable to detect a statistically significant sample ofwarm debris disks due to its limited sensitivity at 12 ?m. UsingTycho-2 Spectral Catalog stars previously shown to exhibit 8 ?mmid-IR circumstellar excesses confirmed at 24 ?m in the SpitzerGalactic Legacy Infrared MidPlane Survey Extraordinaire (GLIMPSE)survey, we investigate the frequency of mid-IR excesses amongintermediate-mass (2-4 M sun) stars in a completevolume-limited sample. Our study of 338 stars is four times larger thana complete sample of 12 ?m sources from the IRAS Point SourceCatalog. We find that 0.3% ± 0.3% of intermediate-mass starsexhibit a signature of a possible terrestrial-temperature debris disksat wavelengths of 8 ?m and greater. We also find that 1.2% ±0.6% of intermediate-mass stars exhibit evidence for circumstellar disksundergoing inner disk clearing, i.e., candidate transition disk systems.Using stellar lifetimes and the frequency of transition and primordialdisks within a given spectral type, we find that pre-main-sequence disksaround intermediate-mass stars dissipate in 5 ± 2 Myr, consistentwith other studies.
| A GLIMPSE into the Nature of Galactic Mid-IR Excesses
We investigate the nature of the mid-IR excess for 31 intermediate-massstars that exhibit an 8 μm excess in either the Galactic LegacyInfrared Mid-Plane Survey Extraordinaire or the Mid-Course SpaceExperiment using high-resolution optical spectra to identify starssurrounded by warm circumstellar dust. From these data we determineprojected stellar rotational velocities and estimate stellar effectivetemperatures for the sample. We estimate stellar ages from thesetemperatures, parallactic distances, and evolutionary models. Using MIPS[24] measurements and stellar parameters we determine the nature of theinfrared excess for 19 GLIMPSE stars. We find that 15 stars exhibitHα emission and four exhibit Hα absorption. Assuming thatthe mid-IR excesses arise in circumstellar disks, we use the Hαfluxes to model and estimate the relative contributions of dust andfree-free emission. Six stars exhibit Hα fluxes that implyfree-free emission can plausibly explain the infrared excess at [24].These stars are candidate classical Be stars. Nine stars exhibitHα emission, but their Hα fluxes are insufficient to explainthe infrared excesses at [24], suggesting the presence of acircumstellar dust component. After the removal of the free-freecomponent in these sources, we determine probable disk dust temperaturesof Tdisk~=300-800 K and fractional infrared luminosities ofLIR/L*~=10-3. These nine stars may bepre-main-sequence stars with transitional disks undergoing diskclearing. Three of the four sources showing Hα absorption exhibitcircumstellar disk temperatures ~=300-400 K,LIR/L*~=10-3, IR colors K-[24]<3.3,and are warm debris disk candidates. One of the four Hα absorptionsources has K-[24]>3.3 implying an optically thick outer disk and isa transition disk candidate.
| Spectroscopic analysis of southern B and Be stars
Spectroscopic monitoring of 141 southern field B-type stars, 114 of themknown to exhibit the Be phenomenon, allowed the estimation of theirprojected rotational velocities, effective temperatures and superficialgravities from both line and equivalent width fitting procedures.Stellar ages, masses and bolometric luminosities were derived frominternal structure models. Without taking into account the effects ofgravity darkening, we note the occurrence of the Be phenomenon in laterstages of main-sequence phase.
| Physical Parameters of Southern B- and Be-Type Stars
In this paper we present new results on stellar fundamental parametersfor early B and Be field stars observed in the southern hemisphere:effective temperature, superficial gravity, and projected stellarrotation velocity. The estimation of their projected rotation velocitiesis made by two successive methods. We first obtain an initial valuebased on Fourier transforms of the He I λ4471 line for 34 B andBe field stars with magnitudes in the range0.5<=mv<=10, followed by a more accurate fittingprocedure of observed lines with non-LTE model line profiles. Thisprocedure yields stellar rotation velocity estimates that are inagreement with those of the literature. We derive also Teffand logg values by fitting equivalent widths and profiles of NLTE modelspectra to the observed ones. Finally, we give estimates of stellarages, masses, and bolometric luminosities derived from interpolations inthe evolutionary tracks calculated by Schaller.
| A Catalogue of Be-Stars
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| Observations of southern emission-line stars
A catalog of 1929 stars showing H-alpha emission on photographic platesis presented which covers the entire southern sky south of declination-25 deg to a red limiting magnitude of about 11.0. The catalog providesprevious designations of known emission-line stars equatorial (1900) andgalactic coordinates, visual and photographic magnitudes, H-alphaemission parameters, spectral types, and notes on unusual spectralfeatures. The objects listed include 16 M stars, 25 S stars, 37 carbonstars, 20 symbiotic stars, 40 confirmed or suspected T Tauri stars, 16novae, 14 planetary nebulae, 11 P Cygni stars, 9 Bep stars, 87 confirmedor suspected Wolf-Rayet stars, and 26 'peculiar' stars. Two new Tassociations are discovered, one in Lupus and one in Chamaeleon. Objectswith variations in continuum or H-alpha intensity are noted, and thedistribution by spectral type is analyzed. It is found that the skydistribution of these emission-line stars shows significantconcentrations in the region of the small Sagittarius cloud and in theCarina region.
| A spectral survey of the southern Milky Way 1 : general description and catalogue 1 (l=306 -318 degrees).
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974A&AS...16..445S&db_key=AST
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