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Title: High-resolution H -band Spectroscopy of Be Stars with SDSS-III/APOGEE. II. Line Profile and Radial Velocity Variability

Abstract

We report on the H -band spectral variability of classical Be stars observed over the course of the Apache Point Galactic Evolution Experiment (APOGEE), one of four subsurveys comprising SDSS-III. As described in the first paper of this series, the APOGEE B-type emission-line (ABE) star sample was culled from the large number of blue stars observed as telluric standards during APOGEE observations. In this paper, we explore the multi-epoch ABE sample, consisting of 1100 spectra for 213 stars. These “snapshots” of the circumstellar disk activity have revealed a wealth of temporal variability including, but not limited to, gradual disappearance of the line emission and vice versa over both short and long timescales. Other forms of variability include variation in emission strength, emission peak intensity ratios, and emission peak separations. We also analyze radial velocities (RVs) of the emission lines for a subsample of 162 stars with sufficiently strong features, and we discuss on a case-by-case basis whether the RV variability exhibited by some stars is caused by binary motion versus dynamical processes in the circumstellar disks. Ten systems are identified as convincing candidates for binary Be stars with as of yet undetected companions.

Authors:
;  [1];  [2];  [3]; ;  [4];  [5];  [6];  [7];  [8]; ;  [9];  [10];  [11];  [12]
  1. Apache Point Observatory and New Mexico State University, P.O. Box 59, Sunspot, NM, 88349-0059 (United States)
  2. Department of Physics and Astronomy, The University of Oklahoma, 440 W. Brooks Street, Norman, OK 73019 (United States)
  3. Department of Physics, Austin College, 900 N. Grand Avenue, Sherman, TX 75090 (United States)
  4. Department of Physics, Lehigh University, Bethlehem, PA 18015 (United States)
  5. Observatório Nacional, Rua General José Cristino 77, 20921-400, São Cristovão, Rio de Janeiro (Brazil)
  6. Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road Shanghai 200030 (China)
  7. Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904-4325 (United States)
  8. Center for Astrophysics and Space Astronomy, Department of Astrophysical and Planetary Sciences, University of Colorado, 389 UCB, Boulder, Colorado 80309-0389 (United States)
  9. Departamento de Astronomía, Universidad de Concepción, Concepción (Chile)
  10. Departamento de Física, Facultad de Ciencias, Universidad de La Serena, Cisternas 1200, La Serena (Chile)
  11. Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802 (United States)
  12. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD, 21218 (United States)
Publication Date:
OSTI Identifier:
22663723
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astronomical Journal (Online); Journal Volume: 153; Journal Issue: 4; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION SPECTRA; ABSORPTION SPECTROSCOPY; EMISSION; GALACTIC EVOLUTION; RADIAL VELOCITY; RESOLUTION; STARS; VARIATIONS

Citation Formats

Chojnowski, S. Drew, Holtzman, Jon A., Wisniewski, John P., Whelan, David G., Labadie-Bartz, Jonathan, Pepper, Joshua, Fernandes, Marcelo Borges, Lin, Chien-Cheng, Majewski, Steven R., Stringfellow, Guy S., Mennickent, Ronald E., Tang, Baitian, Roman-Lopes, Alexandre, Hearty, Fred R., and Zasowski, Gail. High-resolution H -band Spectroscopy of Be Stars with SDSS-III/APOGEE. II. Line Profile and Radial Velocity Variability. United States: N. p., 2017. Web. doi:10.3847/1538-3881/AA64CE.
Chojnowski, S. Drew, Holtzman, Jon A., Wisniewski, John P., Whelan, David G., Labadie-Bartz, Jonathan, Pepper, Joshua, Fernandes, Marcelo Borges, Lin, Chien-Cheng, Majewski, Steven R., Stringfellow, Guy S., Mennickent, Ronald E., Tang, Baitian, Roman-Lopes, Alexandre, Hearty, Fred R., & Zasowski, Gail. High-resolution H -band Spectroscopy of Be Stars with SDSS-III/APOGEE. II. Line Profile and Radial Velocity Variability. United States. doi:10.3847/1538-3881/AA64CE.
Chojnowski, S. Drew, Holtzman, Jon A., Wisniewski, John P., Whelan, David G., Labadie-Bartz, Jonathan, Pepper, Joshua, Fernandes, Marcelo Borges, Lin, Chien-Cheng, Majewski, Steven R., Stringfellow, Guy S., Mennickent, Ronald E., Tang, Baitian, Roman-Lopes, Alexandre, Hearty, Fred R., and Zasowski, Gail. Sat . "High-resolution H -band Spectroscopy of Be Stars with SDSS-III/APOGEE. II. Line Profile and Radial Velocity Variability". United States. doi:10.3847/1538-3881/AA64CE.
@article{osti_22663723,
title = {High-resolution H -band Spectroscopy of Be Stars with SDSS-III/APOGEE. II. Line Profile and Radial Velocity Variability},
author = {Chojnowski, S. Drew and Holtzman, Jon A. and Wisniewski, John P. and Whelan, David G. and Labadie-Bartz, Jonathan and Pepper, Joshua and Fernandes, Marcelo Borges and Lin, Chien-Cheng and Majewski, Steven R. and Stringfellow, Guy S. and Mennickent, Ronald E. and Tang, Baitian and Roman-Lopes, Alexandre and Hearty, Fred R. and Zasowski, Gail},
abstractNote = {We report on the H -band spectral variability of classical Be stars observed over the course of the Apache Point Galactic Evolution Experiment (APOGEE), one of four subsurveys comprising SDSS-III. As described in the first paper of this series, the APOGEE B-type emission-line (ABE) star sample was culled from the large number of blue stars observed as telluric standards during APOGEE observations. In this paper, we explore the multi-epoch ABE sample, consisting of 1100 spectra for 213 stars. These “snapshots” of the circumstellar disk activity have revealed a wealth of temporal variability including, but not limited to, gradual disappearance of the line emission and vice versa over both short and long timescales. Other forms of variability include variation in emission strength, emission peak intensity ratios, and emission peak separations. We also analyze radial velocities (RVs) of the emission lines for a subsample of 162 stars with sufficiently strong features, and we discuss on a case-by-case basis whether the RV variability exhibited by some stars is caused by binary motion versus dynamical processes in the circumstellar disks. Ten systems are identified as convincing candidates for binary Be stars with as of yet undetected companions.},
doi = {10.3847/1538-3881/AA64CE},
journal = {Astronomical Journal (Online)},
number = 4,
volume = 153,
place = {United States},
year = {Sat Apr 01 00:00:00 EDT 2017},
month = {Sat Apr 01 00:00:00 EDT 2017}
}
  • The Apache Point Observatory Galactic Evolution Experiment (APOGEE) has amassed the largest ever collection of multi-epoch, high-resolution (R∼22,500), H-band spectra for B-type emission line (Be) stars. These stars were targeted by APOGEE as telluric standard stars and subsequently identified via visual inspection as Be stars based on H i Brackett series emission or shell absorption in addition to otherwise smooth continua and occasionally non-hydrogen emission features. The 128/238 APOGEE Be stars for which emission had never previously been reported serve to increase the total number of known Be stars by ∼6%. Because the H band is relatively unexplored compared tomore » other wavelength regimes, we focus here on identification of the H-band lines and analysis of the emission peak velocity separations (Δv{sub p}) and emission peak intensity ratios (V/R) of the usually double-peaked H i and non-hydrogen emission lines. H i Br11 emission is found to preferentially form in the circumstellar disks at an average distance of ∼2.2 stellar radii. Increasing Δv{sub p} toward the weaker Br12–Br20 lines suggests these lines are formed interior to Br11. By contrast, the observed IR Fe ii emission lines present evidence of having significantly larger formation radii; distinctive phase lags between IR Fe ii and H i Brackett emission lines further supports that these species arise from different radii in Be disks. Several emission lines have been identified for the first time including C i 16895, a prominent feature in the spectra for almost a fifth of the sample and, as inferred from relatively large Δv{sub p} compared to the Br11–Br20, a tracer of the inner regions of Be disks. Emission lines at 15760 Å and 16781 Å remain unidentified, but usually appear along with and always have similar line profile morphology to Fe ii 16878. Unlike the typical metallic lines observed for Be stars in the optical, the H-band metallic lines, such as Fe ii 16878, never exhibit any evidence of shell absorption, even when the H i lines are clearly shell-dominated. The first known example of a quasi-triple-peaked Br11 line profile is reported for HD 253659, one of several stars exhibiting intra- and/or extra-species V/R and radial velocity variation within individual spectra. Br11 profiles are presented for all discussed stars, as are full APOGEE spectra for a portion of the sample.« less
  • We present the H-band spectral line lists adopted by the Apache Point Observatory Galactic Evolution Experiment (APOGEE). The APOGEE line lists comprise astrophysical, theoretical, and laboratory sources from the literature, as well as newly evaluated astrophysical oscillator strengths and damping parameters. We discuss the construction of the APOGEE line list, which is one of the critical inputs for the APOGEE Stellar Parameters and Chemical Abundances Pipeline, and present three different versions that have been used at various stages of the project. The methodology for the newly calculated astrophysical line lists is reviewed. The largest of these three line lists containsmore » 134,457 molecular and atomic transitions. In addition to the format adopted to store the data, the line lists are available in MOOG, Synspec, and Turbospectrum formats. The limitations of the line lists along with guidance for its use on different spectral types are discussed. We also present a list of H-band spectral features that are either poorly represented or completely missing in our line list. This list is based on the average of a large number of spectral fit residuals for APOGEE observations spanning a wide range of stellar parameters.« less
  • The SDSS-III APOGEE collaboration has identified a single useable line in the H-band spectra of APOGEE target stars arising from a singly ionized species. This line of Ti II (λ{sub air} = 15873.84 Å) is therefore of great importance for use in stellar surface gravity, or log(g), determinations via the Saha equation. While a theoretical estimate of the line strength exists, to date no laboratory measurement of the line strength has been reported. Herein we report an absolute laboratory transition probability measurement for this important Ti II line. A relative line strength measurement is made of the Ti II H-band line ofmore » interest and a reference line with a previously reported absolute transition probability. This ratio is measured using multiple spectra of a high-current water-cooled HC lamp recorded with a calibrated FT-IR spectrometer.« less
  • We are carrying out a large ancillary program with the Sloan Digital Sky Survey, SDSS-III, using the fiber-fed multi-object near-infrared APOGEE spectrograph, to obtain high-resolution H-band spectra of more than 1200 M dwarfs. These observations will be used to measure spectroscopic rotational velocities, radial velocities, physical stellar parameters, and variability of the target stars. Here, we describe the target selection for this survey, as well as results from the first year of scientific observations based on spectra that will be publicly available in the SDSS-III DR10 data release. As part of this paper we present radial velocities and rotational velocitiesmore » of over 200 M dwarfs, with a vsin i precision of ∼2 km s{sup –1} and a measurement floor at vsin i = 4 km s{sup –1}. This survey significantly increases the number of M dwarfs studied for rotational velocities and radial velocity variability (at ∼100-200 m s{sup –1}), and will inform and advance the target selection for planned radial velocity and photometric searches for low-mass exoplanets around M dwarfs, such as the Habitable Zone Planet Finder, CARMENES, and TESS. Multiple epochs of radial velocity observations enable us to identify short period binaries, and adaptive optics imaging of a subset of stars enables the detection of possible stellar companions at larger separations. The high-resolution APOGEE spectra, covering the entire H band, provide the opportunity to measure physical stellar parameters such as effective temperatures and metallicities for many of these stars. At the culmination of this survey, we will have obtained multi-epoch spectra and radial velocities for over 1400 stars spanning the spectral range M0-L0, providing the largest set of near-infrared M dwarf spectra at high resolution, and more than doubling the number of known spectroscopic vsin i values for M dwarfs. Furthermore, by modeling telluric lines to correct for small instrumental radial velocity shifts, we hope to achieve a relative velocity precision floor of 50 m s{sup –1} for bright M dwarfs. With three or more epochs, this precision is adequate to detect substellar companions, including giant planets with short orbital periods, and flag them for higher-cadence followup. We present preliminary, and promising, results of this telluric modeling technique in this paper.« less
  • The authors report high-resolution spectroscopy of 125 field stars previously observed as part of the Sloan Digital Sky Survey and its program for Galactic studies, the Sloan Extension for Galactic Understanding and Exploration (SEGUE). These spectra are used to measure radial velocities and to derive atmospheric parameters, which they compare with those reported by the SEGUE Stellar Parameter Pipeline (SSPP). The SSPP obtains estimates of these quantities based on SDSS ugriz photometry and low-resolution (R {approx} 2000) spectroscopy. For F- and G-type stars observed with high signal-to-noise ratios (S/N), they empirically determine the typical random uncertainties in the radial velocities,more » effective temperatures, surface gravities, and metallicities delivered by the SSPP to be 2.4 km s{sup -1}, 130 K (2.2%), 0.21 dex, and 0.11 dex, respectively, with systematic uncertainties of a similar magnitude in the effective temperatures and metallicities. They estimate random errors for lower S/N spectra based on numerical simulations.« less