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 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 [-17/6] Mean Br11 equivalent width WBr11
(in Å) (G3)
65- 68 F4.2 0.1nm e_ [0/2.93] Standard deviation (σ) in
(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 [-93/76.6]? Mean radial velocity (G4)
81- 84 F4.1 km/s e_ [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_ [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 2015AJ....149....7C, Cat. J/AJ/149/7
(End) Prepared by [AAS]; Sylvain Guehenneux [CDS] 03-Aug-2017