J/A+A/609/A7 Of-type stars in N206 in the LMC (Ramachandran+, 2018)
Stellar population of the superbubble N 206 in the LMC.
I. Analysis of the Of-type stars.
Ramachandran V., Hainich R., Hamann W.-R., Oskinova L.M., Shenar T.,
Sander A.A.C., Todt H., Gallagher J.S.
<Astron. Astrophys., 609, A7 (2018)>
=2018A&A...609A...7R 2018A&A...609A...7R (SIMBAD/NED BibCode)
ADC_Keywords: Magellanic Clouds ; Stars, OB ; MK spectral classification
Keywords: stars: early-type - Magellanic Clouds - stars: atmospheres -
stars: winds, outflows - stars: mass-loss - stars: massive
Abstract:
Massive stars severely influence their environment by their
strong ionizing radiation and by the momentum and kinetic energy input
provided by their stellar winds and supernovae. Quantitative analyses
of massive stars are required to understand how their feedback creates
and shapes large scale structures of the interstellar medium. The
giant HII region N 206 in the Large Magellanic Cloud contains an OB
association that powers a superbubble filled with hot X-ray emitting
gas, serving as an ideal laboratory in this context.
We aim to estimate stellar and wind parameters of all OB stars in N
206 by means of quantitative spectroscopic analyses. In this first
paper, we focus on the nine Of-type stars located in this region. We
determine their ionizing flux and wind mechanical energy. The analysis
of nitrogen abundances in our sample probes rotational mixing.
We obtained optical spectra with the multi-object spectrograph FLAMES
at the ESO-VLT. When possible, the optical spectroscopy was
complemented by UV spectra from the HST, IUE, and FUSE archives.
Detailed spectral classifications are presented for our sample Of-type
stars. For the quantitative spectroscopic analysis we used the Potsdam
Wolf-Rayet model atmosphere code. We determined the physical
parameters and nitrogen abundances of our sample stars by fitting
synthetic spectra to the observations.
The stellar and wind parameters of nine Of-type stars, which are
largely derived from spectral analysis are used to construct wind
momentum - luminosity relationship. We find that our sample follows a
relation close to the theoretical prediction, assuming clumped winds.
The most massive star in the N 206 association is an Of supergiant
that has a very high mass-loss rate. Two objects in our sample reveal
composite spectra, showing that the Of primaries have companions of
late O subtype. All stars in our sample have an evolutionary age of
less than 4 million yr, with the O2-type star being the youngest. All
these stars show a systematic discrepancy between evolutionary and
spectroscopic masses. All stars in our sample are nitrogen enriched.
Nitrogen enrichment shows a clear correlation with increasing
projected rotational velocities.
The mechanical energy input from the Of stars alone is comparable to
the energy stored in the N 206 superbubble as measured from the
observed X-ray and Hα emission.
Description:
We observed the complete massive star population associated with the
N206 superbubble on 2015 December 19-20 with VLT-FLAMES. The
observation was carried out using three of the standard settings of
the Giraffe spectrograph LR02 (resolving power R=6000, 3960-4567Å),
LR03 (R=7500, 4501-5071Å), and HR15N (R=19200, 6442-6817Å),
respectively. We took three to six exposures (30 min each) for each
pointing in three spectrograph setting to improve the S/N. Ultraviolet
(UV) spectra are available for three Of stars in our sample, and we
retrieved these from the Mikulski Archive for Space Telescopes
(MAST3). The stellar and wind parameters of individual OB stars
derived from spectral analysis using PoWR models.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 150 11 Stellar parameters of nine Of-type stars in
N206 superbubble
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See also:
J/A+A/615/A40 : OB stars in N206 in the LMC (Ramachandran+, 2018)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- N206-FS Catalog number
4 A1 --- m_N206-FS [ab] Multiplicity index on N206-FS
6 A1 --- n_N206-FS Note on N206-FS (1)
8- 11 F4.1 kK Teff Temperature
13- 16 F4.2 [Lsun] logL Luminosity
18- 20 F3.1 [cm/s2] logg Gravity
22- 26 F5.2 [Msun/yr] logdM/dt Mass-loss rate
28- 31 F4.2 mag E(B-V) Color excess
33- 37 F5.2 mag VMAG Absolute visual magnitude
39- 42 F4.1 Rsun R Stellar radius
44- 47 I4 km/s vinf Terminal velocity
49 A1 --- n_vinf [7] Note on vinf (2)
51- 53 I3 km/s vsini Projected rotational velocity
55- 57 I3 Msun M Stellar mass (spectroscopic mass)
59- 62 F4.1 [s-1] logQ Rate of hydrogen ionizing photons
64- 67 F4.2 [Lsun] logLmec Mechanical luminosity
69- 81 A13 --- SpType Spectral and luminosity class
83 I1 h RAh Right ascension (J2000) (3)
85- 86 I2 min RAm Right ascension (J2000) (3)
88- 93 F6.3 s RAs Right ascension (J2000) (3)
95 A1 --- DE- Declination sign (J2000) (3)
96- 97 I2 deg DEd Declination (J2000) (3)
99-100 I2 arcmin DEm Declination (J2000) (3)
102-106 F5.2 arcsec DEs Declination (J2000) (3)
108-150 A43 --- OName Other names, from Simbad (3)
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Note (1): Notes as follows:
2 = Primary component
3 = Secondary component
5 = When strong clumping (D=20 and RD=0.05R*) is adopted then
logdM/dt=-5.59M☉/yr and logLmec=3.05L☉. The X-ray field is
included in this model, with X-ray luminosity LX=4.7x1033erg/s.
6 = When strong clumping (D=20 and RD=0.05R*) is adopted then
logdM/dt=-5.72M☉/yr and logLmec=2.92L☉. The X-ray field is
included in this model, with X-ray luminosity LX=1.7x1033erg/s.
Note (2): Note on Vinf as follows:
7 = Vinf is determined from UV P-Cygni profiles. Other values are
theoretically calculated from vesc.
Note (3): From table 1 of the paper.
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Acknowledgements:
Varsha Ramachandran, varsha(at)astro.physik.uni-potsdam.de
References:
Ramachandran et al., Paper II 2018A&A...615A..40R 2018A&A...615A..40R, Cat. J/A+A/615/A40
(End) Patricia Vannier [CDS] 10-Apr-2019