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Title: High-resolution H-band spectroscopy of Be stars with SDSS-III/apogee. I. New Be stars, line identifications, and line profiles

Abstract

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 to 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 andmore » 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

Authors:
; ; ; ; ; ;  [1];  [2];  [3];  [4];  [5]; ; ; ;  [6];  [7];  [8];  [9];  [10];  [11] more »; « less
+ Show Author Affiliations
  1. Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904-4325 (United States)
  2. Department of Physics, Austin College, 900 N. Grand Ave., Sherman, TX 75090 (United States)
  3. Department of Physics and Astronomy, The University of Oklahoma, 440 W. Brooks St., Norman, OK 73019 (United States)
  4. Department of Astronomy, The University of Texas at Austin, 2515 Speedway, Stop C1400 Austin, Texas 78712-1205 (United States)
  5. Department of Astronomy, University of Florida, 211 Bryant Space Science Center, Gainesville, FL 32611-2055 (United States)
  6. Apache Point Observatory and New Mexico State University, P.O. Box 59, Sunspot, NM, 88349-0059 (United States)
  7. ELTE Gothard Astrophysical Observatory, 1H-9704 Szombathely, Szent Imre herceg st. 112 (Hungary)
  8. Department of Astronomy, University of Michigan, 830 Dennison, 500 Church St., Ann Arbor, MI 48109-1042 (United States)
  9. Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802 (United States)
  10. Department of Physics and Astronomy, Johns Hopkins University, Bloomberg Center for Physics and Astronomy, Room 366, 3400 N. Charles Street, Baltimore, MD 21218 (United States)
  11. Institute for Gravitation and the Cosmos, The Pennsylvania State University, University Park, PA 16802 (United States)
Publication Date:
OSTI Identifier:
22342158
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astronomical Journal (New York, N.Y. Online); Journal Volume: 149; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION; COMPARATIVE EVALUATIONS; DISTANCE; EMISSION; GALACTIC EVOLUTION; HYDROGEN; INSPECTION; ISOCHRONOUS CYCLOTRONS; RADIAL VELOCITY; RESOLUTION; SPECTRA; SPECTROSCOPY; STARS; VARIATIONS; WAVELENGTHS

Citation Formats

Chojnowski, S. Drew, Majewski, Steven R., Hall, Matthew, Beaton, Rachael, Burton, Adam, Damke, Guillermo, Wilson, John, Whelan, David G., Wisniewski, John P., Shetrone, Matthew, Eikenberry, Steve, Hasselquist, Sten, Holtzman, Jon A., Brewington, Howard, Brinkmann, J., Mészáros, Szabolcs, Nidever, David, Schneider, Donald P., Zasowski, Gail, Bizyaev, Dmitry, E-mail: drewski@virginia.edu, and and others. High-resolution H-band spectroscopy of Be stars with SDSS-III/apogee. I. New Be stars, line identifications, and line profiles. United States: N. p., 2015. Web. doi:10.1088/0004-6256/149/1/7.
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Chojnowski, S. Drew, Majewski, Steven R., Hall, Matthew, Beaton, Rachael, Burton, Adam, Damke, Guillermo, Wilson, John, Whelan, David G., Wisniewski, John P., Shetrone, Matthew, Eikenberry, Steve, Hasselquist, Sten, Holtzman, Jon A., Brewington, Howard, Brinkmann, J., Mészáros, Szabolcs, Nidever, David, Schneider, Donald P., Zasowski, Gail, Bizyaev, Dmitry, E-mail: drewski@virginia.edu, & and others. High-resolution H-band spectroscopy of Be stars with SDSS-III/apogee. I. New Be stars, line identifications, and line profiles. United States. doi:10.1088/0004-6256/149/1/7.
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Chojnowski, S. Drew, Majewski, Steven R., Hall, Matthew, Beaton, Rachael, Burton, Adam, Damke, Guillermo, Wilson, John, Whelan, David G., Wisniewski, John P., Shetrone, Matthew, Eikenberry, Steve, Hasselquist, Sten, Holtzman, Jon A., Brewington, Howard, Brinkmann, J., Mészáros, Szabolcs, Nidever, David, Schneider, Donald P., Zasowski, Gail, Bizyaev, Dmitry, E-mail: drewski@virginia.edu, and and others. Thu . "High-resolution H-band spectroscopy of Be stars with SDSS-III/apogee. I. New Be stars, line identifications, and line profiles". United States. doi:10.1088/0004-6256/149/1/7.
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@article{osti_22342158,
title = {High-resolution H-band spectroscopy of Be stars with SDSS-III/apogee. I. New Be stars, line identifications, and line profiles},
author = {Chojnowski, S. Drew and Majewski, Steven R. and Hall, Matthew and Beaton, Rachael and Burton, Adam and Damke, Guillermo and Wilson, John and Whelan, David G. and Wisniewski, John P. and Shetrone, Matthew and Eikenberry, Steve and Hasselquist, Sten and Holtzman, Jon A. and Brewington, Howard and Brinkmann, J. and Mészáros, Szabolcs and Nidever, David and Schneider, Donald P. and Zasowski, Gail and Bizyaev, Dmitry, E-mail: drewski@virginia.edu and and others},
abstractNote = {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 to 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.},
doi = {10.1088/0004-6256/149/1/7},
journal = {Astronomical Journal (New York, N.Y. Online)},
number = 1,
volume = 149,
place = {United States},
year = {Thu Jan 01 00:00:00 EST 2015},
month = {Thu Jan 01 00:00:00 EST 2015}
}
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Journal Article:
DOI:  10.1088/0004-6256/149/1/7
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  • ; ; ; ... - Astronomical Journal (Online)
    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 ofmore » 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.« less

  • ; ; ; ... - Astrophysical Journal, Supplement Series
    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

  • ; ; - Astrophysical Journal Letters
    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

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  • ; ; ; ... - Astronomical Journal (New York, N.Y. Online)
    Chemical compositions are determined based on high-resolution spectroscopy for 137 candidate extremely metal-poor (EMP) stars selected from the Sloan Digital Sky Survey (SDSS) and its first stellar extension, the Sloan Extension for Galactic Understanding and Exploration (SEGUE). High-resolution spectra with moderate signal-to-noise (S/N) ratios were obtained with the High Dispersion Spectrograph of the Subaru Telescope. Most of the sample (approximately 80%) are main-sequence turnoff stars, including dwarfs and subgiants. Four cool main-sequence stars, the most metal-deficient such stars known, are included in the remaining sample. Good agreement is found between effective temperatures estimated by the SEGUE stellar parameter pipeline, basedmore » on the SDSS/SEGUE medium-resolution spectra, and those estimated from the broadband (V - K){sub 0} and (g - r){sub 0} colors. Our abundance measurements reveal that 70 stars in our sample have [Fe/H] < -3, adding a significant number of EMP stars to the currently known sample. Our analyses determine the abundances of eight elements (C, Na, Mg, Ca, Ti, Cr, Sr, and Ba) in addition to Fe. The fraction of carbon-enhanced metal-poor stars ([C/Fe] > +0.7) among the 25 giants in our sample is as high as 36%, while only a lower limit on the fraction (9%) is estimated for turnoff stars. This paper is the first of a series of papers based on these observational results. The following papers in this series will discuss the higher-resolution and higher-S/N observations of a subset of this sample, the metallicity distribution function, binarity, and correlations between the chemical composition and kinematics of extremely metal-poor stars.« less