J/AJ/156/257 Spectroscopy of RGB stars in Draco & Ursa Minor (Spencer+, 2018)
The binary fraction of stars in dwarf galaxies: the cases of Draco
and Ursa Minor.
Spencer M.E., Mateo M., Olszewski E.W., Walker M.G., McConnachie A.W.,
Kirby E.N.
<Astron. J., 156, 257 (2018)>
=2018AJ....156..257S 2018AJ....156..257S
ADC_Keywords: Galaxies, nearby ; Stars, double and multiple ; Stars, giant ;
Spectroscopy ; Effective temperatures ; Abundances, [Fe/H] ;
Radial velocities
Keywords: binaries: general - galaxies: dwarf -
galaxies: individual (Draco, Ursa Minor) -
galaxies: kinematics and dynamics
Abstract:
Measuring the frequency of binary stars in dwarf spheroidal galaxies
(dSphs) requires data taken over long time intervals. We combine radial
velocity measurements from five literature sources taken over the course
of ∼30 years to yield the largest multi-epoch kinematic sample for stars
in the dSphs Draco and Ursa Minor. With this data set, we are able to
implement an improved version of the Bayesian technique described in
Spencer et al. (2017, J/AJ/153/254) to evaluate the binary fraction of
red giant stars in these dwarf galaxies. Assuming Duquennoy & Mayor
(1991A&A...248..485D 1991A&A...248..485D) period and mass ratio distributions, the binary
fractions in Draco and Ursa Minor are 0.50-0.06+0.04 and
0.78-0.08+0.09, respectively. We find that a normal mass ratio
distribution is preferred over a flat distribution, and that log-normal
period distributions centered on long periods (µlogP>3.5) are
preferred over distributions centered on short ones. We reanalyzed the
binary fractions in Leo II, Carina, Fornax, Sculptor, and Sextans, and
find that there is <1% chance that binary fraction is a constant quantity
across all seven dwarfs, unless the period distribution varies greatly.
This indicates that the binary populations in Milky Way dSphs are not
identical in regard to their binary fractions, period distributions, or
both. We consider many different properties of the dwarfs (e.g., mass,
radius, luminosity, etc.) and find that binary fraction might be larger
in dwarfs that formed their stars quickly and/or have high velocity
dispersions.
Description:
Before compiling a broader sample using previous studies, we first present
new data from our spectroscopic observations of individual red giant branch
(RGB) candidates in Ursa Minor, acquired using the Hectochelle multi-fiber
spectrograph (Szentgyorgyi 2006NewAR..50..326S 2006NewAR..50..326S) at the MMT on Mount Hopkins,
Arizona. The observational setup (wavelength range 5160-5280 Å, resolving
power R∼20000) and data reduction procedures are identical to those that
Walker et al. (2015, J/MNRAS/448/2717) describe in detail for our previous
study of Draco.
Our analysis aims to define the binary fractions in Draco and Ursa Minor
via the presence of velocity variability among the stars. Data must meet
several criteria to be used in this analysis. There are six data sets each
for Draco and Ursa Minor that meet our criteria. In Draco there are 692
unique member stars, 341 of which have multiple observations. There are a
total of 1204 velocity measurements for the subset of stars with multiple
observations. These data are listed in Table 3. In Ursa Minor there are 680
unique member stars. A total of 284 of them have multiple observations.
There are a total of 875 measurements for the stars with multiple
observations, which are listed in Table 4.
Objects:
------------------------------------------------------------
RA (ICRS) DE Designation(s)
------------------------------------------------------------
17 20 14.33 +57 55 16.4 Draco = NAME Draco Galaxy
15 09 11.34 +67 12 51.7 Ursa Minor = NAME UMi Galaxy
------------------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 116 1407 New MMT/Hectochelle data from individual
observations of RGB candidates in Ursa Minor
table2m.dat 65 973 Hectochelle weighted means for stars with
multiple observations
table3.dat 67 1204 Velocities of RGB stars in Draco
table4.dat 67 875 Velocities of RGB stars in Ursa Minor
list.dat 80 2233 List of spectra for Ursa Minor
umisp/* . 2233 Individual fits spectra
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See also:
J/AJ/110/2131 : M/L for Draco and UMi. I. (Armandroff+ 1995)
J/AJ/121/841 : RV photometry of Draco dwarf spheroidal galaxy
(Piatek+, 2001)
J/AJ/123/2511 : RV photometry of Draco dwarf spheroidal galaxy
(Piatek+, 2002)
J/AJ/124/3222 : VI photometry of Draco and UMi galaxies (Bellazzini+, 2002)
J/MNRAS/330/792 : Radial velocity in Draco (Kleyna+, 2002)
J/ApJ/617/L41 : Red giant variable candidates in UMi dSph (Mighell+, 2004)
J/ApJS/191/352 : Abundances in stars of Milky Way dwarf satellites
(Kirby+, 2010)
J/AJ/144/4 : Properties of dwarf galaxies in the Local Group
(McConnachie+, 2012)
J/MNRAS/448/2717 : Bayesian analysis of resolved stellar spectra
(Walker+, 2015)
J/ApJ/821/54 : XMM spectral analysis of Draco dSph (Sonbas+, 2016)
J/AJ/153/254 : Velocities of RGB stars in the Leo II dwarf galaxy
(Spencer+, 2017)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 h RAh Hour of Right Ascension (J2000)
4- 5 I2 min RAm Minute of Right Ascension (J2000)
7- 11 F5.2 s RAs Second of Right Ascension (J2000)
13 A1 --- DE- Sign of the Declination (J2000)
14- 15 I2 deg DEd Degree of Declination (J2000)
17- 18 I2 arcmin DEm Arcminute of Declination (J2000)
20- 23 F4.1 arcsec DEs Arcsecond of Declination (J2000)
25- 34 F10.2 d HJD Heliocentric Julian Date
36- 39 F4.1 --- S/N [0.3/45.7] Median signal-to-noise ratio
per pixel
41- 46 F6.1 km/s vlos [-444.5/82.3] Line-of-sight velocity (G1)
48- 50 F3.1 km/s e_vlos [0.4/3.8] Uncertainty in vlos
52- 55 F4.1 --- S-vlos [-0.6/0.7] The vlos skewness (1)
57- 59 F3.1 --- K-vlos [2.4/4] The vlos kurtosis (1)
61- 64 I4 K Teff [4308/7472] Effective temperature
66- 69 I4 K e_Teff [50/1137] Uncertainty in Teff
71- 74 F4.1 --- S-Teff [-0.9/3.5] The Teff skewness (1)
76- 79 F4.1 --- K-Teff [1.8/21.5] The Teff kurtosis (1)
81- 83 F3.1 [cm/s2] log(g) [0.7/5.6] Log surface gravity
85- 87 F3.1 [cm/s2] e_log(g) [0.1/1.3] Uncertainty in log(g)
89- 92 F4.1 --- S-log(g) [-2/1.7] The log(g) skewness (1)
94- 96 F3.1 --- K-log(g) [1.9/8.3] The log(g) kurtosis (1)
98-102 F5.2 [Sun] [Fe/H] [-3.53/1.19] Metallicity
104-107 F4.2 [Sun] e_[Fe/H] [0.05/1.08] Uncertainty in [Fe/H]
109-112 F4.1 --- S-[Fe/H] [-1.2/1.7] The [Fe/H] skewness (1)
114-116 F3.1 --- K-[Fe/H] [1.6/9.3] The [Fe/H] kurtosis (1)
--------------------------------------------------------------------------------
Note (1): Of the posterior probability distribution function.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2m.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 h RAh Hour of Right Ascension (J2000)
4- 5 I2 min RAm Minute of Right Ascension (J2000)
7- 11 F5.2 s RAs Second of Right Ascension (J2000)
13 A1 --- DE- Sign of the Declination (J2000)
14- 15 I2 deg DEd Degree of Declination (J2000)
17- 18 I2 arcmin DEm Arcminute of Declination (J2000)
20- 23 F4.1 arcsec DEs Arcsecond of Declination (J2000)
25- 30 F6.1 km/s vlosmean [-444.5/82.3] Weighted mean line-of-sight
velocity (G1)
32- 34 F3.1 km/s e_vlosmean [0.2/3.5] Uncertainty in vlosmean
36- 39 I4 K Teffmean [4315/7302] Weighted mean effective
temperature
41- 44 I4 K e_Teffmean [25/1137] Uncertainty in Teffmean
46- 48 F3.1 [cm/s2] log(g)mean [0.7/5.6] Weighted mean log surface gravity
50- 52 F3.1 [cm/s2] e_log(g)mean [0.1/1.3] Uncertainty in log(g)mean
54- 58 F5.2 [Sun] [Fe/H]mean [-3.53/1.19] Weighted mean metallicity
60- 63 F4.2 [Sun] e_[Fe/H]mean [0.03/1.08] Uncertainty in [Fe/H]mean
65 I1 --- Nobs [1/5] Number of independent observations
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 13 A13 --- ID Star identifier
15- 16 I2 --- NRV [2/11] Number of velocities for ID
18- 19 I2 h RAh Hour of Right Ascension (J2000)
21- 22 I2 min RAm Minute of Right Ascension (J2000)
24- 28 F5.2 s RAs Second of Right Ascension (J2000)
29 A1 --- DE- Sign of the Declination (J2000)
30- 31 I2 deg DEd Degree of Declination (J2000)
33- 34 I2 arcmin DEm Arcminute of Declination (J2000)
36- 40 F5.2 arcsec DEs Arcsecond of Declination (J2000)
42- 50 F9.1 d HJD Heliocentric Julian Date
52- 57 F6.1 km/s RV [-335.9/-206.7] Radial velocity (1)
59- 62 F4.1 km/s e_RV [0.2/11.8] Uncertainty in RV
64- 67 A4 --- r_RV Reference from which the velocity measurement
originated (2)
--------------------------------------------------------------------------------
Note (1): After correcting for systematic offsets. Only stars with multi-epoch
velocity measurements are included.
Note (2): Reference code as follows:
A95 = Armandroff et al. (1995, J/AJ/110/2131);
K02 = Kleyna et al. (2002, J/MNRAS/330/792);
K03 = Kleyna et al. (2003ApJ...588L..21K 2003ApJ...588L..21K);
K10 = Kirby et al. (2010, J/ApJS/191/352);
O95 = Olszewski et al. (1995AJ....110.2120O 1995AJ....110.2120O);
W04 = Wilkinson et al. (2004ApJ...611L..21W 2004ApJ...611L..21W);
W15 = Walker et al. (2015, J/MNRAS/448/2717);
Tab2 = Table 2 of this article.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 F10.6 deg RAdeg Right Ascension in decimal degrees (J2000)
12- 22 F11.6 deg DEdeg Declination in decimal degrees (J2000)
24- 34 F11.3 d HJD Heliocentric Julian Date of observation
36- 80 A45 --- FileName Name of FITS file in subdirectory umisp (1)
--------------------------------------------------------------------------------
Note (1): Individual fits files are included for all individual spectroscopic
targets and are named raAAA.AAAAAAdecBBBB.BBBBBBhjdCCCCCCC.CCC.fits, where:
AAA.AAAAAA = right ascension of target (degrees);
BBBB.BBBBBB = declination of target (degrees);
CCCCCCC.CCC = heliocentric julian date of observation (days).
Each fits file includes the following fields:
radeg: right ascension (degrees);
decdeg: declination (degrees);
hjd: heliocentric julian date (days);
snratio: median signal to noise ratio per pixel;
vmoments: four-element array containing mean (km/s), variance (km2/s2),
skewness and kurtosis of posterior PDF for velocitiy;
teffmoments: four-element array containing mean (K), variance (K2),
skewness and kurtosis of posterior PDF for Teff;
loggmoments: four-element array containing mean (dex), variance (dex2),
skewness and kurtosis of posterior PDF for logg;
fehmoments: four-element array containing mean (dex), variance (dex2),
skewness and kurtosis of posterior PDF for [Fe/H];
pdfsample: 16x1000-element array containing 1000 random draws from the
15-dimensional posterior PDF generated by MultiNest
(Feroz & Hobson, 2008MNRAS.384..449F 2008MNRAS.384..449F; 2009MNRAS.398.1601F 2009MNRAS.398.1601F; see
below for labels of each dimension);
lambda: wavelength (angstroms);
skysub: sky-subtracted spectrum;
varskysub: variance in skysub;
bestfit: best-fitting model spectrum.
The 16x1000-element array in the 'pdfsample' field contains 1000 random draws
from the 15-dimensional posterior PDF generated by MultiNest. The quantities
listed in each of the sixteen dimensions are (see Walker et al. 2015,
J/MNRAS/448/2717 for details of model):
1. velocity (km/s)
2. Teff (K)
3. logg (dex)
4. [Fe/H] (dex)
5. p0
6. p1
7. p2
8. p3
9. p4
10. p5
11. h (angstroms)
12. q1 (km/s)
13. q2 (km/s)
14. s2
15. s1
16. log-likelihood
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Global notes:
Note (G1): In heliocentric rest frame.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 15-Apr-2019