J/ApJ/754/69 UV spectroscopy of solar-mass stars (Linsky+, 2012)
Ultraviolet spectroscopy of rapidly rotating solar-mass stars: emission-line
redshifts as a test of the solar-stellar connection.
Linsky J.L., Bushinsky R., Ayres T., France K.
<Astrophys. J., 754, 69 (2012)>
=2012ApJ...754...69L 2012ApJ...754...69L
ADC_Keywords: Spectra, ultraviolet ; Stars, F-type ; Stars, G-type ;
Radial velocities
Keywords: stars: activity; stars: chromospheres; stars: rotation;
stars: solar-type; Sun: chromosphere; Sun: UV radiation
Abstract:
We compare high-resolution ultraviolet spectra of the Sun and thirteen
solar-mass main-sequence stars with different rotational periods that
serve as proxies for their different ages and magnetic field
structures. In this, the second paper in the series, we study the
dependence of ultraviolet emission-line centroid velocities on stellar
rotation period, as rotation rates decrease from that of the Pleiades
star HII314 (Prot=1.47days) to α Cen A (Prot=28days). Our
stellar sample of F9 V to G5 V stars consists of six stars observed
with the Cosmic Origins Spectrograph on the Hubble Space Telescope
(HST) and eight stars observed with the Space Telescope Imaging
Spectrograph on HST. We find a systematic trend of increasing redshift
with more rapid rotation (decreasing rotation period) that is similar
to the increase in line redshift between quiet and plage regions on
the Sun. The fastest-rotating solar-mass star in our study, HII314,
shows significantly enhanced redshifts at all temperatures above
logT=4.6, including the corona, which is very different from the
redshift pattern observed in the more slowly rotating stars. This
difference in the redshift pattern suggests that a qualitative change
in the magnetic-heating process occurs near Prot=2days. We propose
that HII314 is an example of a solar-mass star with a magnetic heating
rate too large for the physical processes responsible for the redshift
pattern to operate in the same way as for the more slowly rotating
stars. HII314 may therefore lie above the high activity end of the set
of solar-like phenomena that is often called the "solar-stellar
connection."
Description:
We have searched the MAST archive and the StarCAT STIS spectral
catalog (Ayres 2010, Cat. J/ApJS/187/149) for UV spectra
(1150-1600Å) of solar-mass stars, which for this study are defined
as those stars with spectral types between F9 V and G5 V. We identify
13 stars observed with the COS G130M and STIS E140M and E140H gratings
that, including the Sun, we call the high-resolution group. One star,
χ1 Ori, was observed by both COS and STIS. The spectral
resolving powers R=λ/Δλ=17000 (COS G130M), 45000
(STIS E140M), and 114000 (STIS E140H) allow us to analyze line-profile
shapes and Doppler shifts.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table5.dat 83 18 Emission line redshifts using the ClI 1351Å
line as a fiducial mark for the photospheric
radial velocity
table6.dat 161 515 Emission line profile parameters
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See also:
B/hst : HST Archived Exposures Catalog (STScI, 2007)
J/ApJS/187/149 : StarCAT: STIS UV echelle spectra of stars (Ayres, 2010)
J/A+A/493/1099 : CaII HK emission in rapidly rotating stars (Schroeder+, 2009)
J/A+A/415/331 : HST/STIS spectra of alpha Cen A (Pagano+, 2004)
J/A+A/397/147 : Activity-rotation relationship in stars (Pizzolato+ 2003)
Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 14 A14 --- Name Star name
16- 21 A6 --- SpT MK spectral type
23- 27 A5 --- Inst Instrument (1)
29- 30 A2 --- f_Prot Limit or uncertainty flag on Prot
32- 37 F6.2 d Prot [1.4/28]? Rotational period
39- 44 F6.2 --- V(SiIV) [-19/66]? SiIV (λ1393) velocity (2)
46- 51 F6.2 --- V(CIV) [-18/40]? CIV (λ1548) velocity (2)
53- 58 F6.2 --- V(ClI) [-31/53]? ClI (λ1351.657) velocity
60- 65 F6.2 --- V(Si-Cl)c [10/22]? COS velocity difference
(V(SiIV)-V(ClI)) (3)
67 A1 --- u_V(Si-Cl)s [~] Uncertainty flag on V(Si-Cl)s
69- 74 F6.2 --- V(Si-Cl)s [2.3/16.3] STIS velocity difference
(V(SiIV)-V(ClI))
76 A1 --- u_V(C-Cl) [~] Uncertainty flag on V(C-Cl)
78- 83 F6.2 --- V(C-Cl) [2.6/13]? STIS velocity difference
(V(CIV)-V(ClI))
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Note (1): Instruments are:
COS = Cosmic Origins Spectrograph
HRTS = High Resolution Telescope and Spectrometer
STIS = Space Telescope Imaging Spectrograph
(velocities were measured from the StarCAT database)
SUMER = Solar Ultraviolet Measurements of Emitted Radiation on SOHO
Note (2): The SiIV velocities are flux-weighted averages of the central
velocities of single-Gaussian fits to the SiIV(1393) and (1402) lines,
and the CIV velocities are corresponding flux-weighted averages for
the CIV(1548) and (1550) lines. These velocities are measured relative
to the ClI(1351) line, which we treat as representative of the
photospheric velocity (see Section 2.4) to correct for errors in
centering the star in the COS entrance aperture.
Note (3): COS velocity differences (V(SiIV)-V(ClI)) are corrected to the
STIS scale (in STARCat) by subtracting 5.45km/s based on the
comparison of χ1 Ori COS and STIS spectra. We use the centroid
velocities of single Gaussian fits to the emission lines.
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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- 14 A14 --- Name Star name
16- 19 A4 --- Inst HST Instrument
21- 27 A7 --- Ion Ion identifier (1)
29- 37 F9.4 0.1nm lam.0 Laboratory wavelength; in Angstroms (2)
38- 39 A2 --- f_lam.0 [bl ] blend (3)
41- 49 F9.4 0.1nm lam.n ? Narrow component wavelength; in Angstroms
51- 56 F6.4 0.1nm e_lam.n ? Uncertainty in lam.n
58- 64 F7.2 km/s dV.n ? Narrow component radial velocity Δvn
66- 70 F5.2 km/s e_dV.n ? Uncertainty in dV.n
72 A1 --- l_Fluxn Limit flag on Fluxn
73- 80 F8.3 10-19W/m2 Fluxn Narrow component flux; 1e-16 erg/s/cm2
82- 87 F6.2 10-19W/m2 e_Fluxn ? Uncertainty in Fluxn
89- 95 F7.2 km/s FWHMn ? Narrow component Full-Width at Half-Maximum
96 A1 --- f_FWHMn [)] assumed value of FWHMn (4)
98-102 F5.2 km/s e_FWHMn ? Uncertainty in FWHMn
104-113 F10.5 0.1nm lam.b ? Broad component wavelength; in Angstroms
115-120 F6.4 0.1nm e_lam.b ? Uncertainty in lam.b
122-127 F6.2 km/s dV.b ? Broad component radial velocity Δvb
129-133 F5.2 km/s e_dV.b ? Uncertainty in dV.b
135-141 F7.2 10-19W/m2 Fluxb ? Broad component flux; 1e-16 erg/s/cm2
143-148 F6.2 10-19W/m2 e_Fluxb ? Uncertainty in Fluxb
150-155 F6.2 km/s FWHMb ? Broad component Full-Width at Half-Maximum
157-161 F5.2 km/s e_FWHMb ? Uncertainty in FWHMb
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Note (1): The asterisk after the ion indicates that we computed a two-Gaussian
fit to the emission line. For two stars (HII314 and HD 209458) the COS
observations with the G130M and G160M gratings were taken at different
times with the star likely placed in different portions of the aperture.
For this reason the velocity scales for the two gratings are different.
In both cases these are the lines after Cl.I.
Note (2): Given by Morton (1991ApJS...77..119M 1991ApJS...77..119M) when available or by Pagano
et al. (2004, Cat. J/A+A/415/331).
Note (3):
bl = close blend of lines from the same ion for which we use the mean
laboratory wavelength. Widely separated blends or blends involving
more than one atom or ion are not included.
Note (4):
) = assumed FWHM for the undetected coronal FeXII (1242.00, 1349.36)
and FeXXI (1354.080) lines. See text.
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History:
From electronic version of the journal
References:
Linsky et al. Paper I. 2012ApJ...745...25L 2012ApJ...745...25L
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 03-Mar-2014