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J/AJ/153/174 SDSS-III/APOGEE. II. The multi-epoch ABE sample (Chojnowski+, 2017)

High-resolution H-band spectroscopy of Be stars with SDSS-III/APOGEE. II. Line profile and radial velocity variability. Chojnowski S.D., Wisniewski J.P., Whelan D.G., Labadie-Bartz J., Borges Fernandes M., Lin C.-C., Majewski S.R., Stringfellow G.S., Mennickent R.E., Roman-Lopes A., Tang B., Hearty F.R., Holtzman J.A., Pepper J., Zasowski G. <Astron. J., 153, 174-174 (2017)> =2017AJ....153..174C (SIMBAD/NED BibCode)
ADC_Keywords: Stars, Be ; Stars, emission ; Equivalent widths ; Radial velocities Keywords: circumstellar matter - infrared: stars - stars: early-type - stars: emission-line, Be - stars: peculiar - stars: variables: general 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. Description: The Apache Point Observatory Galactic Evolution Experiment (APOGEE) instrument is a 300-fiber spectrograph that records most of the H band with resolving power R∼22500 on three non-overlapping detectors (blue detector: 15145-15810Å, green detector: 15860-16430Å, red detector: 16480-16950Å). The SDSS-IV/APOGEE-2 survey began operations on the 2.5m Sloan telescope starting in 2014 August. Although numerous new Be stars have been identified in the APOGEE-2 telluric standard star sample, in this paper we only use APOGEE-2 spectra pertaining to Be stars that are also observed during SDSS-III/APOGEE-1 and again selected as telluric standards for APOGEE-2 observations. In particular, the following stars have been observed during APOGEE-1 and APOGEE-2, with the number of APOGEE-2 observations given in parentheses: ABE-038 (1), ABE-051 (1), ABE-054 (6), ABE-074 (15), ABE-093 (6), ABE-101 (5), ABE-148 (1), ABE-167 (4), ABE-176 (6), ABE-177 (6), ABE-184 (6), ABE-185 (6), ABE-187 (7), ABE-188 (7), and ABE-190 (7). After rejecting (1) spectra with S/N<40, (2) spectra mentioned in Section 2.1.2, and (3) 16 stars with only one APOGEE observation, we arrive at a total of 1100 spectra for 213 stars in this paper (more than five spectra per star on average). File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 45 3 *Additional new Be stars from APOGEE1 table2.dat 101 213 *APOGEE B-type emission-line (ABE) visit summary table3.dat 110 1101 *APOGEE B-type emission-line (ABE) star summary
Note on table1.dat,table2.dat,table3.dat: APOGEE=Apache Point Observatory Galactic Evolution Experiment.
See also: V/137 : Extended Hipparcos Compilation (XHIP) (Anderson+, 2012) J/AJ/149/7 : SDSS-III/APOGEE. I. Be stars (Chojnowski+, 2015) J/ApJ/786/120 : Spectropolarimetry of classical Be stars (Draper+, 2014) J/ApJ/709/1306 : Spectropolarimetry of 60 Cyg and π Aqr (Wisniewski+, 2010) J/A+A/451/1053 : Fundamental parameters of Be stars (Fremat+, 2006) J/MNRAS/371/252 : Southern B and Be stars (Levenhagen+, 2006) J/A+A/415/145 : Radial velocities of 16 stars in NGC 6913 (Boeche+, 2004) J/A+A/368/912 : Polarization and rotational vel. of Be stars (Yudin, 2001) Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 3 A3 --- ABE Identifier of the APOGEE B-type emission-line (ABE) star 5- 10 F6.3 mag Hmag H-band magnitude 12 I1 --- Ns Number of spectra 14- 21 A8 --- Morph Morphology (1) 23- 24 I2 h RAh Hour of Right Ascension (J2000) 26- 27 I2 min RAm Minute of Right Ascension (J2000) 29- 33 F5.2 s RAs Second of Right Ascension (J2000) 35 A1 --- DE- Sign of the Declination 36- 37 I2 deg DEd Degree of Declination (J2000) 39- 40 I2 arcmin DEm Arcminute of Declination (J2000) 42- 45 F4.1 arcsec DEs Arcsecond of Declination (J2000)
Note (1): "weak em." means double-peaked emission that is fully contained within broad photospheric absorption.
Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 3 A3 --- ABE Identifier of the Apache Point Observatory Galactic Evolution Experiment (APOGEE) B-type emission-line (ABE) star (running number) (G1) 5- 21 A17 --- Name Star name 23- 24 I2 --- Nobs [2/30] Number of APOGEE observations 26- 30 I5 d MJD0 [55702/56812] Modified Julian Date (MJD) of first APOGEE observation (JD-2400000.5) 32- 35 I4 d dJD [1/1862] Observational baseline (ΔJD) 37- 39 I3 --- <S/N> [46/800] Mean Signal-to-Noise ratio 41- 48 A8 --- VType Variability classification (1) 50- 52 I3 km/s <PSep> [0/629]? Mean Br11 peak separation (G2) 54- 56 I3 km/s PAmp [0/128]? Scatter (maximum minus minimum) in Br11 peak separation 58- 63 F6.2 0.1nm <EW> [-17/6] Mean Br11 equivalent width WBr11 (in Å) (G3) 65- 68 F4.2 0.1nm e_<EW> [0/2.93] Standard deviation (σ) in <EW> (in Å) 70- 73 F4.2 0.1nm EWAmp [0.01/8.37] Scatter (maximum minus minimum) in Br11 equivalent width (in Å) 75- 79 F5.1 km/s <RV> [-93/76.6]? Mean radial velocity (G4) 81- 84 F4.1 km/s e_<RV> [0.2/14.4]? Mean standard deviation (σ) of line-by-line radial velocities 86- 90 F5.1 km/s RVAmp [0/112.9]? Scatter (maximum minus minimum) in radial velocity 92- 94 F3.1 --- o_<RV> [3/9]? Mean number of H-Br lines used for radial velocity determination (G5) 96-101 A6 --- RVType Type of radial velocity measurement, as described in Section 3.4 (double, shell, or single) (G6)
Note (1): Variability classification is defined as follows: RV = The scatter in radial velocity measurements exceeds twice the average standard deviation of individual H-Br lines measurements. A total of 37 stars are classified as RV-variable; W = Either the standard deviation of WBr11 measurements was greater than 0.65Å, or else that visual inspection clearly indicates variable emission strength despite a small standard deviation in multi-epoch WBr11 measurements. A total of 30 stars are classified as WBr11-variable; V/R = The ratio of intensities of V and R peaks is variable. The classification is assigned based on visual inspection of the spectra to confirm that the V/R ratio changed in multiple H-Br lines. A total of 16 stars are classified as V/R-variable; TD = 'Transient Disk', and indicates the APOGEE spectra include at least one mostly emission-less spectrum. The classification is assigned based on visual inspection of the spectra. A total of 18 stars are classified as having transient disks.
Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
1- 3 A3 --- ABE Identifier of the Apache Point Observatory Galactic Evolution Experiment (APOGEE) B-type emission-line (ABE) star (running number) (G1) 5- 21 A17 --- Name Star name 23- 40 A18 --- Visit Visit identifier (ap#-Plate-MJD-Fiber) (1) 42- 62 A21 --- Date UT date of mid-observation (ISO 8601 date time) 64- 74 F11.5 d MJD [55701.9/57701.6] Modified Julian Date (MJD) of mid-observation (JD-2400000.5) 76- 79 I4 --- S/N [41/1427] APOGEE spectra Signal-to-Noise ratio 81- 83 I3 km/s PSep [0/629]? Br11 peak separation (G2) 85- 90 F6.2 0.1nm EW [-18.4/6.4]? Br11 equivalent width WBr11 (in Å) (G3) 92- 96 F5.1 km/s RV [-95.3/98.3]? Radial velocity derived from the H-Br lines (G4) 98-101 F4.1 km/s e_RV [0.1/22.9]? Standard deviation (σ) of line-by-line radial velocities 103 I1 --- o_RV [3/9]? Number of H-Br lines used for RV (G5) 105-110 A6 --- RVType Type of radial velocity measurement, as described in Section 3.4 (single, double, or shell) (G6)
Note (1): The visit identifier, which begins with "ap1" for APOGEE1 spectra and "ap2" for APOGEE2 spectra, and which is followed by the plug-plate number, the observation MJD (JD-2400000), and the fiber number.
Global Notes: Note (G1): The ABE identifiers used take one of two forms: * Three-digit identifiers for Be stars serving as APOGEE telluric standard stars; * Two-digit identifiers with an "A" prefix for a sample of 36 previously known stars we intentionally targeted with APOGEE through an ancillary science program. Note (G2): Br11=16811Å, hydrogen Brackett series (H-Br) line. For the 174 stars with double-peaked emission, the violet (V) and red (R) peak positions of the H-Br lines were estimated visually via an interactive plotting routine. The velocity difference between V and R peaks gives the peak separation, and the mean velocity of V and R peaks generally corresponds to the central velocity of the overall line profile. For 61 stars, it was only possible to measure the Br11 peak positions because the emission peaks disappear for weaker H-Br lines. Note (G3): The Br11 16811Å equivalent width (WBr11) was measured via direct summation of the line depth in a 100Å window centered on the Br11 line, with a window width selected so as to encompass the full Br11 profile for all stars, including some continuum adjacent to the broad photospheric absorption wings, when present. Spectra pertaining to fiber numbers 27 and 28 were excluded because a cluster of bad pixels coincides with the position of Br11. For the 31 stars with emission in the 16781Å line (an unidentified line discussed in Paper I, Chojnowski et al. 2015, Cat. J/AJ/149/7) and Fe II 16791Å, WBr11 includes the fluxes of these typically weak lines. Please refer to Section 3.1 for additional details. Note (G4): The first step in our radial velocity measurement process was to discard the portion of the sample (51 out of 213 stars) with very weak H-Br features. We focused on a sample of 162 of the 213 stars with sufficiently sharp H-Br shell absorption or emission peaks that a central velocity could be confidently measured from at least three H-Br lines. The heliocentric radial velocities reported in this paper are the average from all H-Br lines used. Note (G5): The maximum number of spectral lines used per spectrum was 9 (Br11-Br18, Br20), excluding Br19 because of an overlapping diffuse interstellar band (see Figure 4 of Chojnowski et al. 2015, Cat. J/AJ/149/7). The same H-Br lines were typically used for all spectra of a given star, but contamination from airglow and/or telluric residuals and bad pixels were occasionally severe enough in certain spectra to prevent use of the same lines in all spectra. Furthermore, useful lines in one spectrum are not guaranteed to be useful in all spectra because of the temporal variation of the emission strength. Note (G6): RV sample includes three basic line profile types defined as follows: double = double-peaked emission; single = single-peaked emission; shell = shell absorption.
History: From electronic version of the journal References: Chojnowski et al., Paper I 2015AJ....149....7C, Cat. J/AJ/149/7
(End) Prepared by [AAS]; Sylvain Guehenneux [CDS] 03-Aug-2017
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