J/MNRAS/492/2161 Local RR Lyrae stars: native and alien (Zinn+, 2020)
Local RR Lyrae stars: native and alien.
Zinn R., Chen X., Layden A.C., Casetti-Dinescu D.I.
<Mon. Not. R. Astron. Soc., 492, 2161-2176 (2020)>
=2020MNRAS.492.2161Z 2020MNRAS.492.2161Z (SIMBAD/NED BibCode)
ADC_Keywords: Stars, variable ; Milky Way ; Spectra, optical ; Photometry ;
Equivalent widths ; Space velocities
Keywords: stars: variables: RR Lyrae - Galaxy: formation -
Galaxy: kinematics and dynamics
Abstract:
Measurements of [Fe/H] and radial velocity are presented for 89 RR
Lyrae (RRL) candidates within 6kpc of the Sun. After the removal of
two suspected non-RRLs, these stars were added to an existing data
base, which yielded 464 RRLs with [Fe/H] on a homogeneous scale. Using
data from the Gaia satellite (Data Release 2), we calculated the
positions and space velocities for this sample. These data confirm the
existence of a thin disc of RRL with [α/Fe]∼solar. The majority
of the halo RRLs with large total energies have near-zero angular
momenta about the Z-axis. Kinematically, these stars closely resemble
the Gaia-Sausage/Gaia-Enceladus stars that others have proposed are
debris from the merger of a large galaxy with the Milky Way. The
metallicity and period distributions of the RRLs and their positions
in the period-amplitude diagram suggest that this disrupted galaxy was
as massive as the Large Magellanic Cloud and possibly greater.
Description:
A sample of about 100 ab-type RRL was selected from the ASAS online
catalogue (http://www.astrouw.edu.pl/asas/). Queue-scheduled
observations were requested on the 1.5m telescope and Cassegrain
Spectrograph located on Cerro Tololo in Chile and operated by the
Small and Moderate Aperture Research Telescope System (SMARTS)
Consortium. The Loral 1K CCD was used with grating 26/Ia at a tilt of
16.14°, providing spectra covering 3650-5400Å at 1.47Å/pix
resolution.
For most observations, HeAr comparison spectra were taken immediately
before and after a set of three stellar exposures (30-240s each). In
total, 171 such 'visits' were made to 89 separate RRL stars between
2009 August and 2011 February, yielding 525 useable spectra. Table 1
lists, by their ASAS catalogue names, the 89 RRL stars observed.
The ASAS project (Pojmanski 2002AcA....52..397P 2002AcA....52..397P, Cat. II/264) used a
2048x2048 pixel CCD behind a 200mm, f/2.8 camera lens to obtain
time-series, wide-field, low-resolution, V-band images across most of
the Southern sky. We downloaded the photometric data for each star
(magnitude versus time) from the ASAS website. For consistency, we
used the magnitude from aperture #2 for each observation. We rejected
photometry characterized by grades other than 'A' or 'B', leaving many
hundreds of individual observations per star.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 69 89 Coordinates and reddening
table2.dat 79 89 ASAS photometry
table3.dat 87 171 RRL standardized equivalent widths
table4.dat 76 89 Final spectroscopic data
table5.dat 91 464 The sample of Local RR Lyrae stars
table6.dat 94 464 The Galactic positions and the kinematics of
the stars
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See also:
II/264 : ASAS Variable Stars in Southern hemisphere
(Pojmanski+, 2002-2005)
J/AJ/108/1016 : Kinematics of local RR lyrae stars. I. (Layden, 1994)
J/MNRAS/435/3206 : Properties of field RR Lyrae variables (Dambis+, 2013)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 13 A13 --- Name ASAS name (JHHMMSS+DDMM.m)
15- 25 F11.7 deg RAdeg Right ascension (J2000)
27- 37 F11.7 deg DEdeg Declination (J2000)
39- 44 F6.2 deg GLON Galactic longitude
46- 51 F6.2 deg GLAT Galactic latitude
53- 57 F5.3 --- E(B-V) Colour excess
59- 67 A9 --- OName Alternative name
69 I1 --- n_Name [1/3]? Note on the object (1)
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Note (1): Note as follows:
1 = Star not in SPM, used equatorial coordinates from ASAS
2 = Star near LMC, used mean of nearby reddenings, E(B-V)=0.049±0.023mag
3 = Possible c-type RRL
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 13 A13 --- Name ASAS name (JHHMMSS+DDMM.m)
15- 23 A9 --- OName Alternative name
25- 32 F8.6 d Period Variability period
34- 35 I2 10-6d e_Period Error on Period
37- 41 F5.2 mag Vmag Mean V magnitude
43- 47 F5.2 mag Vmax Magnitude V at maximum brightness
49- 53 F5.2 mag Vmin Magnitude V at minimum brightness
55- 58 F4.2 mag RMS RMS scatter of the observed points around the
template T
60 I1 --- T [1/7] Best-fitting template (1)
62- 74 F13.5 d Emax Epoch of maximum light
76- 79 I4 --- Nobs Number of photometric observations
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Note (1): The best-fitting light-curve template is given by T, where T=1-6
indicates RRab stars with different shapes, and T=7 indicates an RRc
template
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 13 A13 --- Name ASAS name (JHHMMSS+DDMM.m)
15- 27 F13.5 d HJD Mean Heliocentric Julian Date of the visit
29- 33 F5.3 --- Phi Photometric phase
35- 39 F5.3 --- e_Phi Error on Phi
41- 44 F4.2 0.1nm EWK0 CaII K equivalent width
46- 49 F4.2 0.1nm e_EWK0 Error on EWK0
51- 55 F5.2 0.1nm EWHd Hδ equivalent width
57- 60 F4.2 0.1nm e_EWHd Error on EWHd
62- 65 F4.2 0.1nm EWHg Hγ equivalent width
67- 70 F4.2 0.1nm e_EWHg Error on EWHg
72- 75 F4.2 0.1nm EWHb Hβ equivalent width
77- 80 F4.2 0.1nm e_EWHb Error on EWHb
82- 85 F4.1 --- S/N Signal to noise ratio
87 I1 --- Nsp [1/6] Number of spectra obtained in the visit
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 13 A13 --- Name ASAS name (JHHMMSS+DDMM.m)
15- 23 A9 --- OName Alternative name
25- 28 F4.2 0.1nm EWKint Equivalent width of the interstellar CaII K
line as described in
Beers (1990AJ.....99..323B 1990AJ.....99..323B)
30- 33 F4.2 0.1nm EWHbz Hβ equivalent width corrected for
interstellar contamination (1)
35- 39 F5.2 [-] [Fe/H] Mean Fe/H abundance ratio for each visit
41- 44 F4.2 [-] e_[Fe/H] Weighted error on [Fe/H]
46- 49 F4.2 [-] s_[Fe/H] Standard deviation of the mean of the [Fe/H]
values from each visit around the mean
51- 53 F3.1 --- Nvis Effective number of visits used
55- 58 I4 km/s vCM ? Centre-of-mass velocity
60- 61 I2 km/s e_vCM ? Error on vCM
63- 64 I2 --- Nfit ? Number of spectra used in the fit
66- 76 A11 --- Com Comment
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Note (1): We calculated the metal-line strength, W(Zβ), using equation
(3) of Layden (1994AJ....108.1016L 1994AJ....108.1016L, Cat. J/AJ/108/1016) and computed
the corrected Hβ equivalent width as
W(Hβz)=W(Hβ)-W(Zβ)
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 18 A18 --- Name RR Lyrae name
20- 29 F10.6 deg RAdeg Right ascension (J2000)
31- 40 F10.6 deg DEdeg Declination (J2000)
42- 48 F7.5 d Period Variability period
50- 53 F4.2 mag Amp Amplitude in the V pass-band
55- 56 A2 --- Type [ab/c ] Variable type
58- 62 F5.2 mag Vmag Mean V magnitude
64- 67 F4.2 mag Vext Interstellar extinctions in the V pass-band
from Dambis et al. (2013MNRAS.435.3206D 2013MNRAS.435.3206D,
Cat. J/MNRAS/435/3206)
69- 73 F5.2 [-] [Fe/H] Fe/H abundance ratio
75 I1 --- r_[Fe/H] [1/4] Source of the metallicity measurement (1)
77 I1 --- N Number of independent studies that contributed
to the listed [Fe/H] value
79- 84 F6.1 km/s vCM Centre-of-mass velocity
86- 89 F4.1 km/s e_vCM Error on vCM
91 I1 --- r_vCM [1/2] Reference for vCM (2)
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Note (1): Reference as follows:
1 = Layden (1994AJ....108.1016L 1994AJ....108.1016L, Cat. J/AJ/108/1016), this paper or the
mean of both. These measurements are from low-resolution spectrograms
following the Layden (1994AJ....108.1016L 1994AJ....108.1016L, Cat. J/AJ/108/1016) technique
2 = Dambis et al. (2013MNRAS.435.3206D 2013MNRAS.435.3206D, Cat. J/MNRAS/435/3206), based on a
transformation to the Layden (1994AJ....108.1016L 1994AJ....108.1016L, Cat. J/AJ/108/1016)
scale
3 = Values transformed to Layden (1994AJ....108.1016L 1994AJ....108.1016L, Cat. J/AJ/108/1016)
scale from high-resolution spectroscopy
4 = Not transformed high-resolution value
Note (2): Reference as follows:
1 = Velocity from literature or this paper
2 = Gaia DR2 (Gaia Collaboration, 2018A&A...616A...1G 2018A&A...616A...1G, Cat. I/345)
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 18 A18 --- Name RR Lyrae name
20- 23 F4.2 kpc Dist Distance
25- 28 F4.2 kpc e_Dist Error on Dist
30- 33 F4.1 kpc X Galactic position X
35- 38 F4.1 kpc Y Galactic position Y
40- 43 F4.1 kpc Z Galactic position Z
45- 48 I4 km/s Vr Radial component of velocity in cylindrical
coordinates
50- 51 I2 km/s e_Vr Error on Vr
53- 56 I4 km/s Vphi Rotational component of velocity in
cylindrical coordinates
58- 60 I3 km/s e_Vphi Error on Vphi
62- 65 I4 km/s Vz Vertical component of velocity in
cylindrical coordinates
67- 68 I2 km/s e_Vz Error on Vz
70- 74 I5 kpc.km/s Lz Angular momentum in z-direction
76- 79 I4 kpc.km/s e_Lz Error on Lz
81- 84 I4 kpc.km/s LT Angular momentum perpendicular to the
z-axis (=sqrt(LX2+LY2))
86- 88 I3 kpc.km/s e_LT Error on LT
90- 94 F5.2 10+5km2/s2 Etot Sum of the kinetic and potential energy of
the star
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History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 17-Mar-2023