J/ApJ/849/150 RR Lyrae candidates in the MW outer halo (Cohen+, 2017)
The outer halo of the Milky Way as probed by RR Lyr variables from the Palomar
Transient Facility.
Cohen J.G., Sesar B., Bahnolzer S., He K., Kulkarni S.R., Prince T.A.,
Bellm E., Laher R.R.
<Astrophys. J., 849, 150 (2017)>
=2017ApJ...849..150C 2017ApJ...849..150C
ADC_Keywords: Stars, variable; Photometry, SDSS; Radial velocities;
Stars, distances
Keywords: Galaxy: halo ; Galaxy: kinematics and dynamics ;
stars: variables: RR Lyrae
Abstract:
RR Lyrae stars are ideal massless tracers that can be used to study
the total mass and dark matter content of the outer halo of the Milky
Way (MW). This is because they are easy to find in the light-curve
databases of large stellar surveys and their distances can be
determined with only knowledge of the light curve. We present here a
sample of 112 RR Lyr stars beyond 50kpc in the outer halo of the MW,
excluding the Sgr streams, for which we have obtained
moderate-resolution spectra with Deimos on the Keck II Telescope. Four
of these have distances exceeding 100kpc. These were selected from a
much larger set of 447 candidate RR Lyr stars that were data-mined
using machine-learning techniques applied to the light curves of
variable stars in the Palomar Transient Facility database. The
observed radial velocities taken at the phase of the variable
corresponding to the time of observation were converted to systemic
radial velocities in the Galactic standard of rest. From our sample of
112 RR Lyr stars we determine the radial velocity dispersion in the
outer halo of the MW to be ∼90km/s at 50kpc, falling to about 65km/s
near 100 kpc once a small number of major outliers are removed. With
reasonable estimates of the completeness of our sample of 447
candidates and assuming a spherical halo, we find that the stellar
density in the outer halo declines as r-4.
Description:
The Palomar Transient Facility (PTF) is a wide-area, two-band (g and R
filters), deep (R∼20.6 single epoch, ∼23mag co-added) survey aimed at
systematic exploration of the optical transient sky. The PTF ran for
3yr, ending 2012 December 31, and then transitioned to the
intermediate-PTF (iPTF). The project uses the CFH12k mosaic camera
mounted on the Palomar Observatory 48-inch Samuel Oschin Schmidt
Telescope. By the end of 2014 September, ∼12000deg2 of sky had been
observed by the iPTF in the Mould R filter (similar in shape to the
SDSS r-band filter, but shifted 27Å redward) and ∼2300deg2 in the
SDSS g' filter at least 30 times each.
A spectroscopic campaign to obtain radial velocities for RR Lyr
candidates began at the Keck Observatory with the Deimos spectrograph
in the spring of 2014 following a brief effort to use the Double
Spectrograph (DBSP) on the Hale Telescope at the Palomar Observatory,
which yielded one useful spectrum.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . this file
table1.dat 63 116 Light curve parameters for RR Lyr candidates
table2.dat 54 116 Radial velocities for RR Lyr candidates
--------------------------------------------------------------------------------
See also:
I/315 : UCAC3 Catalogue (Zacharias+ 2009)
J/MNRAS/375/1381 : Kinematics of RR Lyr and HB stars in NGP (Kinman+, 2007)
J/ApJ/678/851 : RR Lyrae survey in the Galactic Halo (Keller+, 2008)
J/ApJ/678/865 : LONEOS-I RR Lyrae stars (Miceli+, 2008)
J/ApJ/684/1143 : BHB candidates in the Milky Way (Xue+, 2008)
J/ApJ/701/1053 : Abundances of 8 stars in the Draco dSph (Cohen+, 2009)
J/AJ/137/4377 : List of SEGUE plate pairs (Yanny+, 2009)
J/AJ/139/59 : Milky Way halo velocity dispersion profile (Brown+, 2010)
J/ApJ/719/931 : Chemical evolution of the UMi dSph (Cohen+, 2010)
J/ApJ/708/717 : Light curve templates of RR Lyrae stars (Sesar+, 2010)
J/AJ/142/187 : HST obs. of 7 Pop.II variable stars (Benedict+, 2011)
J/ApJ/740/65 : VLA search for 5GHz radio transients (Ofek+, 2011)
J/ApJ/731/4 : Galactic halo as seen by the CFHTLS (Sesar+, 2011)
J/ApJ/738/79 : SDSS-DR8 BHB stars in the Milky Way's halo (Xue+, 2011)
J/AJ/144/114 : Radial velocities of 6 field RR Lyrae (Sesar+, 2012)
J/ApJ/750/99 : The Pan-STARRS1 photometric system (Tonry+, 2012)
J/ApJ/756/23 : V-band follow-up of RR Lyrae from SEKBO (Akhter+, 2012)
J/ApJ/763/32 : Galactic halo RRab stars from CSS (Drake+, 2013)
J/ApJ/776/26 : RRab stars in the Orphan stream distances (Sesar+, 2013)
J/AJ/146/21 : LINEAR. II. Catalog of RR Lyrae stars (Sesar+, 2013)
J/ApJS/213/9 : Catalina Surveys periodic variable stars (Drake+, 2014)
J/ApJ/793/135 : Positions and distances of RR Lyrae stars (Sesar+, 2014)
J/ApJ/784/170 : SEGUE K giant survey. II. Dist. of 6036 stars (Xue+, 2014)
J/ApJ/788/105 : XSTPS RR Lyrae in the north Galactic cap (Faccioli+, 2014)
J/A+A/584/A44 : Photom. classification of QSO from RCS-2 (Carrasco+, 2015)
J/MNRAS/446/2251 : Southern Catalina Survey type-ab RR Lyrae (Torrealba+, 2015)
J/ApJ/817/73 : QSOs & RR Lyrae in PS1 3π Data (Hernitschek+ 2016)
J/ApJ/838/107 : Distances to RRab stars from WISE and Gaia (Sesar+, 2017)
J/ApJ/844/L4 : PS1 RRab for tracing outer Virgo overdensity (Sesar+, 2017)
J/AJ/153/204 : RR Lyrae stars from the PS1 3π survey (Sesar+, 2017)
http://www.ptf.caltech.edu/news/DR3 : The Palomar Transient Facility DR3
http://www.sdss3.org/ : The SDSS-III home page
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 1 A1 --- Sgr Sgr, a=Probable Sgr Stream
3- 12 F10.6 deg RAdeg Right ascension, decimal degrees (J2000)
14- 22 F9.6 deg DEdeg Declination, decimal degrees (J2000)
24- 32 F9.7 d Per [0.4/0.9] Period
34- 41 F8.2 d HJD [55007.9/57538.7] Epoch of maximum light in
heliocentric Julian date; HJD-2400000 (1)
43- 46 F4.2 mag AmpR [0.4/1.2] Amplitude of variation in PTF-R band
48- 52 F5.2 mag Rmag [0/20.7]? Mean PTF-R band AB magnitude
54- 56 I3 --- N(R) [0/723]? Number of PTF-R band epochs star detected
in late 2016
58- 60 I3 --- N(g) [0/385]? Number of PTF-g band epochs star detected
in late 2016
63- 63 I1 --- Qual [0/3]? Quality (2)
--------------------------------------------------------------------------------
Note (1): Epoch of maximum light in heliocentric Julian date - 2400000 days.
This choice, made for ease of computations, requires 7 digits in the
period for accurate phasing at the present epoch
Note (2): Observed R light curve resembles that of a RR Lyr; code as follows:
1 = excellent;
2 = probable;
3 = uncertain.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 1 A1 --- Sgr Sgr, a=Probable Sgr Stream
3- 12 F10.6 deg RAdeg Right ascension, decimal degrees (J2000)
14- 22 F9.6 deg DEdeg Declination, decimal degrees (J2000)
24- 28 F5.1 kpc Dist [50/109.1] Heliocentric distance
30- 30 I1 --- Nsp [1/2] Number of spectra
32- 37 F6.1 km/s RV-GSR [-256.2/224] Radial velocity, Galactic system
of rest (3)
39- 42 F4.1 km/s e_RV-GSR [12/29] Uncertainty in RVel
44- 51 A8 --- Date Approximate RV date of observation MM/YYYY or
MM/DD/YYYY; "dup" = 2 spectra taken
54- 54 A1 --- f_Nsp Flag on spectra taken (4)
--------------------------------------------------------------------------------
Note (3): RV-GSR is corrected to the systemic velocity, then to the
heliocentric velocity, and then to the Galactic system of rest.
Note (4): Flag on spectra taken --
d = A DBSP spectrum taken with the Hale Telescope at Palomar Observatory.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 18-Jun-2018