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81. Stephenson H{alpha} stars
ID:
ivo://CDS.VizieR/J/A+A/402/963
Title:
Stephenson H{alpha} stars
Short Name:
J/A+A/402/963
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of spectroscopic observations for 52 objects from the list of H{alpha} emission stars of Stephenson (1986ApJ...300..779S). Out of six known T Tauri stars observed, five showed H{alpha} in emission and in one (StHa 40), H{alpha} changed from being in absorption to emission over a period of two years, accompanied by photometric and spectral type variability. We confirm the T Tauri nature of one Stephenson object (StHa 48) on the basis of the presence of H{alpha} and H{beta} in emission, Li I {lambda}6708 in absorption, infrared excess and X-ray emission. Among the 52 objects observed, there were other emission line objects: 1 Ke star, 1 BQ[] star, 2 galaxies and 2 Be stars. We present a higher-resolution spectrum of StHa 62 showing permitted and forbidden lines in emission typical of BQ[] stars. Twenty five out of 30 newly observed objects failed to show H{alpha} in emission. We also present 2MASS observations for 112 StHa objects. We suggest three Stephenson objects (StHa 52, 125 and 129) to be YSOs on the basis of 2MASS, IRAS and ROSAT observations. These and all other known YSOs amongst StHa stars are found in regions of star-forming clouds in Taurus, Orion and Ophiuchus. YSOs at high galactic latitudes in other parts of the sky are therefore rare.
82. Structure of Herbig AeBe disks at mas scale
ID:
ivo://CDS.VizieR/J/A+A/599/A85
Title:
Structure of Herbig AeBe disks at mas scale
Short Name:
J/A+A/599/A85
Date:
21 Oct 2021
Publisher:
CDS
Description:
The aims of this article are to infer the radial and vertical structure at ~au scale of these disks, and the properties of the dust grains: composition and characteristic size. We find that dust at the inner rim of the disk has a sublimation temperature Tsub~1800K. A ring structure is confirmed for approximately half the resolved objects; these rings are wide {delta}r/r>=0.5. Such wide rings exclude an inner rim shaped as a vertical wall, or with a rounded shape, and seem to favor an inner rim with a wedge-like cross-section. The inner disk has a thickness z/r~0.2, flaring to z/r~0.5 in the outer part. We confirm the known luminosity-radius relation; a simple physical model is consistent with both the mean luminosity-radius relation and the ring relative width; however, a significant spread around the mean relation is present. We find in some of the objects a halo component, fully resolved at the shortest interferometer spacing, that is related to the HAeBe class.
83. UBVRI photometry of 131 Herbig Ae/Be
ID:
ivo://CDS.VizieR/J/AJ/126/2971
Title:
UBVRI photometry of 131 Herbig Ae/Be
Short Name:
J/AJ/126/2971
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a new catalog of 108 Herbig Ae/Be candidate stars identified in the Pico dos Dias Survey (Gregorio-Hete et al., 1992AJ....103..549G; Torres et al., 1995AJ....109.2146T and 1999, Special Publ. 10, Rio de Janeiro: Obs. Nac.), together with 19 previously known candidates and four objects selected from the IRAS Faint Source Catalog (<II/156>). These 131 stars were observed with low- and/or medium-resolution spectroscopy, and we complement these data with high-resolution spectra of 39 stars.
84. UV spectra of classical T Tauri stars
ID:
ivo://CDS.VizieR/J/ApJ/784/127
Title:
UV spectra of classical T Tauri stars
Short Name:
J/ApJ/784/127
Date:
21 Oct 2021
Publisher:
CDS
Description:
The far-ultraviolet (FUV; 912-1700 {AA}) radiation field from accreting central stars in classical T Tauri systems influences the disk chemistry during the period of giant planet formation. The FUV field may also play a critical role in determining the evolution of the inner disk (r<10 AU), from a gas- and dust-rich primordial disk to a transitional system where the optically thick warm dust distribution has been depleted. Previous efforts to measure the true stellar+accretion-generated FUV luminosity (both hot gas emission lines and continua) have been complicated by a combination of low-sensitivity and/or low-spectral resolution and did not include the contribution from the bright Ly{alpha} emission line. In this work, we present a high-resolution spectroscopic study of the FUV radiation fields of 16 T Tauri stars whose dust disks display a range of evolutionary states. We include reconstructed Ly{alpha} line profiles and remove atomic and molecular disk emission (from H_2_ and CO fluorescence) to provide robust measurements of both the FUV continuum and hot gas lines (e.g., Ly{alpha}, N V, C IV, He II) for an appreciable sample of T Tauri stars for the first time. We find that the flux of the typical classical T Tauri star FUV radiation field at 1 AU from the central star is ~10^7^ times the average interstellar radiation field. The Ly{alpha} emission line contributes an average of 88% of the total FUV flux, with the FUV continuum accounting for an average of 8%. Both the FUV continuum and Ly{alpha} flux are strongly correlated with C IV flux, suggesting that accretion processes dominate the production of both of these components. On average, only ~0.5% of the total FUV flux is emitted between the Lyman limit (912 {AA}) and the H_2_(0-0) absorption band at 1110 {AA}. The total and component-level high-resolution radiation fields are made publicly available in machine-readable format.
85. Vatican Emission-line stars
ID:
ivo://CDS.VizieR/III/256
Title:
Vatican Emission-line stars
Short Name:
III/256
Date:
21 Oct 2021
Publisher:
CDS
Description:
The survey represents a search for H{alpha} emission-line stars, and was conducted with a 12{deg} objective prism on the Vatican Schmidt telescope. The Vatican Emission Stars (VES) survey covers the galactic plane (|b|<=5{deg}) between galactic longitudes 58 and 174{deg}. The catalog was re-examined by B. Skiff (Lowell Observatory), and tne VES stars were cross-identified with modern surveys: GSC (Cat. I/255), Tycho-2 (I/256), 2MASS (II/246), IRAS point source catalog (II/125), MSX6C (V/114), CMC14 (I/304), GSC-2.3 (I/305), UCAC2 (I/289). Cross-identifications are also supplied with HD/BD/GCVS names, and with Dearborn catalog of red stars (II/68). Many of the stars in the first four papers are not early-type emission-line stars, but instead M giants, where the sharp TiO bandhead at 6544{AA} was mistaken for H-{alpha} emission on the objective-prism plates. Based on the revision of paper V and a later list prepared by Jack MacConnell, a column identifies the "non H-alpha" stars explicitly. The links with the Dearborn, IRAS, and MSX catalogues help identify the red stars. These and other identifications and comments are given in the remarks at the end of each line, or in longer notes in a separate file, indicated by an asterisk (*) next to the star number.
86. VRI photometry in NGC 7129
ID:
ivo://CDS.VizieR/J/AJ/149/200
Title:
VRI photometry in NGC 7129
Short Name:
J/AJ/149/200
Date:
21 Oct 2021
Publisher:
CDS
Description:
NGC7129 is a bright reflection nebula located in the molecular cloud complex near l=105.4{deg}, b=+9.9{deg}, about 1.15kpc distant. Embedded within the reflection nebula is a young cluster dominated by a compact grouping of four early-type stars: BD+65{deg}1638 (B3V), BD+65{deg}1637 (B3e), SVS 13 (B5e), and LkH{alpha} 234 (B8e). About 80 H{alpha} emission sources brighter than V~23 are identified in the region, many of which are presumably T Tauri star members of the cluster. We also present deep (V~23), optical (VR_C_I_C_) photometry of a field centered on the reflection nebula and spectral types for more than 130 sources determined from low dispersion, optical spectroscopy. The narrow pre-main sequence evident in the color-magnitude diagram suggests that star formation was rapid and coeval. A median age of about 1.8Myr is inferred for the H{alpha} and literature-identified X-ray emission sources having established spectral types, using pre-main sequence evolutionary models. Our interpretation of the structure of the molecular cloud and the distribution of young stellar objects is that BD+65{deg}1638 is primarily responsible for evacuating the blister-like cavity within the molecular cloud. LkH{alpha} 234 and several embedded sources evident in near-infrared adaptive optics imaging have formed recently within the ridge of compressed molecular gas. The compact cluster of low-mass stars formed concurrently with the early-type members, concentrated within a central radius of ~0.7pc. Star formation is simultaneously occurring in a semi-circular arc some ~3pc in radius that outlines remaining dense regions of molecular gas. High dispersion, optical spectra are presented for BD+65{deg}1638, BD+65{deg}1637, SVS 13, LkH{alpha} 234, and V350 Cep. These spectra are discussed in the context of the circumstellar environments inferred for these stars.
87. X-ray emission in the Ursa Major stream.
ID:
ivo://CDS.VizieR/J/ApJ/351/492
Title:
X-ray emission in the Ursa Major stream.
Short Name:
J/ApJ/351/492
Date:
21 Oct 2021
Publisher:
CDS
Description:
Results are reported from a comprehensive survey of X-ray emission from stars known or suspected to be members of the UMa cluster and/or stream. Of the 42 UMa member stars surveyed, 18 were detected as X-ray sources, and spectral analysis was performed for 10 stars with sufficient X-ray counts. Consideration is given to relations between X-ray luminosity, color, and kinematics of the sample stars, and the X-ray spectra of the UMa stars are discussed in the context of the general problem of stellar X-ray temperatures. Also confirmed is the lack of X-ray-emitting A dwarfs among UMa members; among stars of later spectral type there is a rather large dispersion in X-ray luminosity. This dispersion cannot readily be explained by contamination with field star interlopers and appears rather to be a property of the UMa X-ray luminosity distribution function.
88. X-ray studies of stars in the Pleiades
ID:
ivo://CDS.VizieR/J/ApJ/348/557
Title:
X-ray studies of stars in the Pleiades
Short Name:
J/ApJ/348/557
Date:
21 Oct 2021
Publisher:
CDS
Description:
Coronal X-ray emission of the Pleiades stars is investigated, and maximum likelihood, integral X-ray luminosity functions are computed for Pleiades members in selected color-index ranges. A detailed search is conducted for long-term variability in the X-ray emission of those stars observed more than once. An overall comparison of the survey results with those of previous surveys confirms the ubiquity of X-ray emission in the Pleiades cluster stars and its higher rate of emission with respect to older stars. It is found that the X-ray emission from dA and early dF stars cannot be proven to be dissimilar to that of Hyades and field stars of the same spectral type. The Pleiades cluster members show a real rise of the X-ray luminosity from dA stars to early dF stars. X-ray emission for the young, solar-like Pleiades stars is about two orders of magnitude more intense than for the nearby solar-like stars.
89. Young intermediate-mass stars in W5
ID:
ivo://CDS.VizieR/J/ApJ/726/18
Title:
Young intermediate-mass stars in W5
Short Name:
J/ApJ/726/18
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of a survey of young intermediate-mass stars (age<5Myr, 1.5M_{sun}_<M*<=15M_{sun}_) in the W5 massive star-forming region. We use combined optical, near-infrared, and Spitzer Space Telescope photometry and optical spectroscopy to define a sample of stars of spectral types A and B and examine their infrared excess properties. We find objects with infrared excesses characteristic of optically thick disks, i.e., Herbig AeBe stars. These stars are rare: <1.5% of the entire spectroscopic sample of A and B stars, and absent among stars more massive than 2.4M_{sun}_. 7.5% of the A and B stars possess infrared excesses in a variety of morphologies that suggest their disks are in some transitional phase between an initial, optically thick accretion state and later evolutionary states. We identify four morphological classes based on the wavelength dependence of the observed excess emission above theoretical photospheric levels: (1) the optically thick disks; (2) disks with an optically thin excess over the wavelength range 2-24um, similar to that shown by Classical Be stars; (3) disks that are optically thin in their inner regions based on their infrared excess at 2-8um and optically thick in their outer regions based on the magnitude of the observed excess emission at 24um; (4) disks that exhibit empty inner regions (no excess emission at {lambda}<8um) and some measurable excess emission at 24um. A sub-class of disks exhibit no significant excess emission at {lambda}<=5.8um, have excess emission only in the Spitzer 8um band and no detection at 24um. We discuss these spectral energy distribution types, and suggest physical models for disks exhibiting these emission patterns and additional observations to test these theories.

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