J/AJ/157/153 Atomic lines in spectra of RR Lyrae & RHB stars (Preston+, 2019)
The axial rotation and variable macroturbulence of RR Lyrae and red horizontal
branch stars.
Preston G.W., Sneden C., Chadid M., Thompson I.B., Shectman S.A.
<Astron. J., 157, 153 (2019)>
=2019AJ....157..153P 2019AJ....157..153P (SIMBAD/NED BibCode)
ADC_Keywords: Stars, variable ; Stars, horizontal branch ; Abundances, [Fe/H] ;
Effective temperatures ; Spectra, optical ; Equivalent widths
Keywords: methods: observational - stars: atmospheres - stars: oscillations -
stars: variables: RR Lyr - techniques: spectroscopic
Abstract:
We have derived relations between FWHMs and equivalent widths of metallic
absorption lines in the spectra of RR Lyrae stars to estimate new upper
limits on the axial equatorial rotational velocities of RR Lyrae and
metal-poor red horizontal branch (RHB) stars. We have also derived the
variations of RR Lyrae macroturbulent velocities during the pulsation
cycles. In RRab cycles, the line widths are dominated by phase-dependent
convolutions of axial rotation and macroturbulence, which we designate
as Vmacrot. The behavior of Vmacrot is remarkably uniform among the
RRab stars, but the behavior of Vmacrot among RRc stars varies strongly
from star to star. The RRab stars exhibit an upper limit on Vmacrot of
5±1 km/s with weak evidence of an anticorrelation with Teff. The RRc
minima range from 2 to 12 km/s. The abrupt decline in large rotations
with decreasing Teff at the blue boundary of the instability strip and
the apparently smooth continuous variation among the RRab and RHB stars
suggests that HB stars gain/lose surface angular momentum on timescales
that are short compared to HB lifetimes. The Vmacrot values for our
metal-poor RHB stars agree well with those derived by Fourier analysis
of an independent but less metal-poor sample of Carney et al.
(2008AJ....135..892C 2008AJ....135..892C); they conform qualitatively to the expectations
of Tanner et al. (2013ApJ...778..117T 2013ApJ...778..117T). A general conclusion of our
investigation is that surface angular momentum as measured by Vrotsin(i)
is not a reliable indicator of total stellar angular momentum anywhere
along the HB.
Description:
The main observational data for this study were provided by several
thousand echelle spectra of 34 RRab stars and 15 RRc stars acquired with
the du Pont 2.5 m telescope of the Las Campanas Observatory in 2006-2014.
The typical spectral resolving power is, as introduced above,
R=λ/Δλ∼27000 at 5000 Å. Exposure times are limited
to small fractions of the stellar pulsation periods, never exceeding
600 s (∼0.01P), and the typical signal-to-noise ratio (S/N) is S/N∼15-20.
The S/N was improved by factors of two or more at all phases by coaddition
of spectra in small phase intervals. Reduction procedures that resulted
in wavelength-calibrated extractions of the du Pont echelle spectra are
described in detail by For et al. (2011, J/ApJS/194/38) and need not be
repeated here. Observations of 24 very metal-poor (MP) RHB field stars
were obtained with the Magellan MIKE spectrograph (Bernstein et al.
2003SPIE.4841.1694B 2003SPIE.4841.1694B) in a mode that delivered R∼40000. The combination
of Magellan's larger aperture and longer exposure times yielded S/N>100
at 5000 Å in all cases. Reductions and analyses of the Magellan/MIKE
spectra are discussed in Preston et al. (2006, J/AJ/132/85).
For this paper, we split the stellar sample into stars that are MP
([Fe/H]< -1) and those that are metal-rich (MR; [Fe/H]>=-1), consistent
with the definition adopted by Chadid et al. (2017ApJ...835..187C 2017ApJ...835..187C) and
Sneden et al. (2017, J/ApJ/848/68; 2018, J/AJ/155/45).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 94 71 The stellar sample
table2.dat 18 187 Atomic lines
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See also:
J/AJ/132/85 : Equivalent width of 33 metal-poor RHB (Preston+, 2006)
J/MNRAS/377/1263 : Multiperiodic RR Lyrae in ASAS catalog (Szczygiel+, 2007)
J/ApJS/194/38 : Radial velocities of 11 field RR Lyrae (For+, 2011)
J/ApJS/197/29 : Chemical compositions of 11 RR Lyrae (For+, 2011)
J/A+A/562/A90 : Times of maximum light of Blazhko RRab stars (Skarka, 2014)
J/MNRAS/445/1584 : AB-type RR Lyrae stars from ASAS and WASP (Skarka, 2014)
J/MNRAS/447/2404 : Equivalent width of 21 RR Lyrae stars (Pancino+, 2015)
J/ApJ/848/68 : Abundances & RVs of stable and Blazhko RRc stars
(Sneden+, 2017)
J/AJ/155/45 : Metal-rich RRc stars in the Carnegie RR Lyrae Survey
(Sneden+, 2018)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 19 A19 --- Group Star group (MP=metal-poor; MR=metal-rich)
21 A1 --- n_Group [bd] Note on Group (1)
23- 35 A13 --- Star Star name
37 A1 --- n_Star [c] Note on Star (2)
39- 43 F5.2 [-] [Fe/H] [-2.92/-0.05]? Metallicity
45- 52 F8.6 d Per [0.235934/0.746568]? Period
54- 61 F8.3 d HJD0 [1869.25/5455.46]? Heliocentric Julian Date
at maximum light (HJD-2450000)
63- 66 F4.1 mag Vmax [8.8/15.1] V magnitude at maximum light
68- 72 F5.3 [K] log(Teff) [3.728/3.851]? Log effective temperature (3)
74- 78 F5.2 km/s FWHMavg [4.8/25.1] Average full-width at half-maximum
of unsaturated lines FWHMunsat
80- 83 F4.2 km/s e_FWHMavg [0.02/2]? Uncertainty in FWHMavg
85- 89 F5.2 km/s Vmacavg [1.3/12.1] Average macroturbulent velocity
Vmacrot
91- 94 F4.2 km/s e_Vmacavg [0.02/1.28]? Uncertainty in Vavg
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Note (1): Note as follows:
b = Nominal periods; see Table 3 and text;
d = Blazhko variation reported by Szczygielstrok & Fabrycky (2007,
J/MNRAS/377/1263).
Note (2): Note as follows:
c = We gathered du Pont echelle spectra for this star but did not include it
in our model atmosphere analyses in previous papers.
Note (3): For the RRab stars, the log Teff values are the means over the
pulsational cycles, as given by Skarka (2014, J/MNRAS/445/1584). For the RRc
stars, we have adopted a constant for log Teff.
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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- 7 F7.2 0.1nm lambda [4045.82/5302.31] Wavelength λ (Å)
9- 13 A5 --- Ion Atomic identification
15- 18 I4 10-13m EW [33/1584] Equivalent width in the Sun (mÅ) (1)
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Note (1): Equivalent widths from the Moore et al. (1966sst..book.....M 1966sst..book.....M) Solar
Atlas.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 15-Jul-2019