- ID:
- ivo://CDS.VizieR/J/ApJ/704/964
- Title:
- Spectroscopic study of Of^+^ supergiants
- Short Name:
- J/ApJ/704/964
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The transition from early Of stars to WN-type objects is poorly understood. O-type supergiants with emission lines (OIf^+^) are considered to be intermediate between these two classes. The scope of this paper is to investigate the spectral variability of three Of^+^ supergiants. We constituted spectral time series of unprecedented quality for our targets (~200 spectra in total), essentially in the blue domain, covering timescales from a few hours up to a few years. Temporal Variance Spectrum and Fourier analyses were performed in order to characterize their spectral variability.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/743/138
- Title:
- Spectroscopic survey of bright white dwarfs
- Short Name:
- J/ApJ/743/138
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have conducted a spectroscopic survey of over 1300 bright (V<=17.5), hydrogen-rich white dwarfs based largely on the last published version of the McCook & Sion (1999ApJS..121....1M, Cat. III/235) catalog. The complete results from our survey, including the spectroscopic analysis of over 1100 DA white dwarfs, are presented. High signal-to-noise ratio optical spectra were obtained for each star and were subsequently analyzed using our standard spectroscopic technique where the observed Balmer line profiles are compared to synthetic spectra computed from the latest generation of model atmospheres appropriate for these stars. First, we present the spectroscopic content of our sample, which includes many misclassifications as well as several DAB, DAZ, and magnetic white dwarfs. Next, we look at how the new Stark broadening profiles affect the determination of the atmospheric parameters. When necessary, specific models and analysis techniques are used to derive the most accurate atmospheric parameters possible. In particular, we employ M dwarf templates to obtain better estimates of the atmospheric parameters for those white dwarfs that are in DA+dM binary systems.
- ID:
- ivo://CDS.VizieR/J/AJ/145/125
- Title:
- Spectroscopy and HST photometry in Westerlund 2
- Short Name:
- J/AJ/145/125
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a spectroscopic and photometric determination of the distance to the young Galactic open cluster Westerlund 2 using WFPC2 imaging from the Hubble Space Telescope (HST) and ground-based optical spectroscopy. HST imaging in the F336W, F439W, F555W, and F814W filters resolved many sources previously undetected in ground-based observations and yielded photometry for 1136 stars. We identified 15 new O-type stars, along with two probable binary systems, including MSP188 (O3+O5.5). We fit reddened spectral energy distributions based on the Padova isochrones to the photometric data to determine individual reddening parameters R_V_ and A_V_for O-type stars in Wd2. We find average values <R_V_>=3.77+/-0.09 and <A_V_>=6.51+/-0.38mag, which result in a smaller distance than most other spectroscopic and photometric studies. After a statistical distance correction accounting for close unresolved binaries (factor of 1.08), our spectroscopic and photometric data on 29 O-type stars yield that Westerlund 2 has a distance <d>=4.16+/-0.07(random)+0.26(systematic)kpc. The cluster's age remains poorly constrained, with an upper limit of 3Myr. Finally, we report evidence of a faint mid-IR polycyclic aromatic hydrocarbon ring surrounding the well-known binary candidate MSP 18, which appears to lie at the center of a secondary stellar grouping within Westerlund 2.
- ID:
- ivo://CDS.VizieR/J/AJ/151/3
- Title:
- Spectroscopy of binary stars
- Short Name:
- J/AJ/151/3
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Young, intermediate-mass stars are experiencing renewed interest as targets for direct-imaging planet searches. However, these types of stars are part of multiple systems more often than not. Close stellar companions affect the formation and orbital architecture of planetary systems, and the properties of the companions can help constrain the binary formation mechanism. Unfortunately, close companions are difficult and expensive to detect with imaging techniques. In this paper, we describe the direct spectral detection method wherein a high-resolution spectrum of the primary is cross-correlated against a template for a companion star. Variants of this method have previously been used to search for stellar, brown dwarf, and even planetary companions. We show that the direct spectral detection method can detect companions as late as M-type orbiting A0 or earlier primary stars in a single epoch on small-aperture telescopes. In addition to estimating the detection limits, we determine the sources of uncertainty in characterizing the companion temperature, and find that large systematic biases can exist. After calibrating the systematic biases with synthetic binary star observations, we apply the method to a sample of 34 known binary systems with an A- or B-type primary star. We detect nine total companions, including four of the five known companions with literature temperatures between 4000K<T<6000K, the temperature range for which our method is optimized. We additionally characterize the companion for the first time in two previously single-lined binary systems and one binary identified with speckle interferometry. This method provides an inexpensive way to use small-aperture telescopes to detect binary companions with moderate mass ratios, and is competitive with high-resolution imaging techniques inside ~100-200mas.
- ID:
- ivo://CDS.VizieR/J/AJ/153/46
- Title:
- Spectroscopy of candidate members in Taurus
- Short Name:
- J/AJ/153/46
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Previous studies have found that ~1deg^2^ fields surrounding the stellar aggregates in the Taurus star-forming region exhibit a surplus of solar-mass stars relative to denser clusters like IC 348 and the Orion Nebula Cluster. To test whether this difference reflects mass segregation in Taurus or a variation in the initial mass function, we have performed a survey for members of Taurus across a large field (~40deg^2^) that was imaged by the Sloan Digital Sky Survey (SDSS). We obtained optical and near-infrared spectra of candidate members identified with those images and the Two Micron All Sky Survey, as well as miscellaneous candidates that were selected with several other diagnostics of membership. We have classified 22 of the candidates as new members of Taurus, which includes one of the coolest known members (M9.75). Our updated census of members within the SDSS field shows a surplus of solar-mass stars relative to clusters, although it is less pronounced than in the smaller fields toward the stellar aggregates that were surveyed for previously measured mass functions in Taurus. In addition to spectra of our new members, we include in our study near-IR spectra of roughly half of the known members of Taurus, which are used to refine their spectral types and extinctions. We also present an updated set of near-IR standard spectra for classifying young stars and brown dwarfs at M and L types.
- ID:
- ivo://CDS.VizieR/J/AJ/149/103
- Title:
- Spectroscopy of candidate YSOs in Serpens
- Short Name:
- J/AJ/149/103
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have completed an optical spectroscopic survey of a sample of candidate young stars in the Serpens Main star-forming region selected from deep B, V, and R band images. While infrared, X-ray, and optical surveys of the cloud have identified many young stellar objects (YSOs), these surveys have been biased toward particular stages of pre-main sequence evolution. We have obtained over 700 moderate resolution optical spectra that, when combined with published data, have led to the identification of 63 association members based on the presence of H{alpha} in emission, lithium absorption, X-ray emission, a mid-infrared excess, and/or reflection nebulosity. Twelve YSOs are identified based on the presence of lithium absorption alone. An additional 16 objects are classified as possible association members and their pre-main sequence nature is in need of confirmation. Spectral types along with V and R band photometry were used to derive effective temperatures and bolometric luminosities for association members to compare with theoretical tracks and isochrones for pre-main sequence stars. An average age of 2Myr is derived for this population. When compared to simulations, there is no obvious evidence for an age spread when considering the major sources of uncertainties in the derived luminosities. However when compared to the young cluster in Ophiuchus, the association members in Serpens appear to have a larger spread in luminosities and hence ages which could be intrinsic to the region or the result of a foreground population of YSOs associated with the Aquila Rift. Modeling of the spectral energy distributions from optical through mid-infrared wavelengths has revealed three new transition disk objects, making a total of six in the cluster. Echelle spectra for a subset of these sources enabled estimates of vsini for seven association members. Analysis of gravity-sensitive lines in the echelle and moderate resolution spectra of the association members indicate surface gravities consistent with dwarf or sub-giant stars.
- ID:
- ivo://CDS.VizieR/J/AJ/147/20
- Title:
- Spectroscopy of 447 nearby M dwarfs
- Short Name:
- J/AJ/147/20
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present metallicities, radial velocities, and near-infrared (NIR) spectral types for 447 M dwarfs determined from moderate resolution (R{approx}2000) NIR spectra obtained with the NASA Infrared Telescope Facility (IRTF)/SpeX. These M dwarfs are primarily targets of the MEarth Survey, a transiting planet survey searching for super Earths around mid-to-late M dwarfs within 33pc. We present NIR spectral types for each star and new spectral templates for the IRTF in the Y, J, H, and K-bands, created using M dwarfs with near-solar metallicities. We developed two spectroscopic distance calibrations that use NIR spectral type or an index based on the curvature of the K-band continuum. Our distance calibration has a scatter of 14%. We searched 27 NIR spectral lines and 10 spectral indices for metallicity sensitive features, taking into account correlated noise in our estimates of the errors on these parameters. We calibrated our relation using 36 M dwarfs in common proper pairs with an F-, G-, or K-type star of known metallicity. We validated the physical association of these pairs using proper motions, radial velocities, and spectroscopic distance estimates. Our resulting metallicity calibration uses the sodium doublet at 2.2{mu}m as the sole indicator for metallicity. It has an accuracy of 0.12dex inferred from the scatter between the metallicities of the primaries and the estimated metallicities of the secondaries. Our relation is valid for NIR spectral types from M1V to M5V and for -1.0dex<[Fe/H]<+0.35dex. We present a new color-color metallicity relation using J-H and J-K colors that directly relates two observables: the distance from the M dwarf main sequence and equivalent width of the sodium line at 2.2{mu}m. We used radial velocities of M dwarf binaries, observations at different epochs, and comparison between our measurements and precisely measured radial velocities to demonstrate a 4km/s accuracy.
- ID:
- ivo://CDS.VizieR/J/ApJ/782/8
- Title:
- Spectroscopy of 104 objects in the ONC
- Short Name:
- J/ApJ/782/8
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We performed low-resolution (R~40) near-infrared (0.9-2.4{mu}m) multi-object spectroscopy of 240 isolated point sources having apparent H-band magnitudes between 9 and 18 in the central 5'x6' of the Orion Trapezium cluster. The observations were performed over four nights at the Canada-France-Hawaii Telescope using the visiting instrument SIMON, an infrared imager and multi-object spectrograph. We present the spectra of 104 objects with accurately derived spectral types including 7 new objects having masses below the hydrogen-burning limit, and 6 objects with masses below the deuterium-burning limit. The spectral classification is performed by fitting previously classified spectral templates of dwarf stars (K4-M3) and optically classified young stellar and substellar objects (M4-L0), to the entire 0.9-2.4{mu}m spectral energy distribution in order to assign a spectral type and visual extinction for each object. Of the 104 objects studied, 44 have been previously classified spectroscopically using various techniques. We perform a rigorous comparison between the previous classifications and our own and find them to be in good agreement. Using the dereddened H-band magnitudes, the classified objects are used to create an Hertzsprung-Russell diagram for the cluster. We find that the previous age estimates of ~1Myr to be consistent with our results. Consistent with previous studies, numerous objects are observed to have luminosities several magnitudes above the 1Myr isochrone. Numerous objects exhibiting emission features in the J band are also reported.
- ID:
- ivo://CDS.VizieR/J/AJ/150/204
- Title:
- Spectroscopy of standard stars
- Short Name:
- J/AJ/150/204
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We define an H{alpha} photometric system that is designed as a companion to the well established H{beta} index. The new system is built on spectrophotometric observations of field stars as well as stars in benchmark open clusters. We present data for 75 field stars, 12 stars from the Coma star cluster, 24 stars from the Hyades, 17 stars from the Pleiades, and 8 stars from NGC 752 to be used as primary standard stars in the new systems. We show that the system transformations are relatively insensitive to the shape of the filter functions. We make comparisons of the H{alpha} index to the H{beta} index and illustrate the relationship between the two systems. In addition, we present relations that relate both hydrogen indices to equivalent width and effective temperature. We derive equations to calibrate both systems for Main Sequence stars with spectral types in the range O9 to K2 for equivalent width and A2 to K2 for effective temperature.
- ID:
- ivo://CDS.VizieR/J/AJ/153/188
- Title:
- Spectroscopy of the foreground population in Orion A
- Short Name:
- J/AJ/153/188
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We perform a spectroscopic survey of the foreground population in Orion A with MMT/Hectospec. We use these data, along with archival spectroscopic data and photometric data, to derive spectral types, extinction values, and masses for 691 stars. Using the Spitzer Space Telescope data, we characterize the disk properties of these sources. We identify 37 new transition disk (TD) objects, 1 globally depleted disk candidate, and 7 probable young debris disks. We discover an object with a mass of less than 0.018-0.030 M_{sun}_, which harbors a flaring disk. Using the H{alpha} emission line, we characterize the accretion activity of the sources with disks, and confirm that the fraction of accreting TDs is lower than that of optically thick disks (46%+/-7% versus 73%+/-9%, respectively). Using kinematic data from the Sloan Digital Sky Survey and APOGEE INfrared Spectroscopy of the Young Nebulous Clusters program (IN-SYNC), we confirm that the foreground population shows similar kinematics to their local molecular clouds and other young stars in the same regions. Using the isochronal ages, we find that the foreground population has a median age of around 1-2 Myr, which is similar to that of other young stars in Orion A. Therefore, our results argue against the presence of a large and old foreground cluster in front of Orion A.
