J/AJ/158/192 He II emission from Wolf-Rayet stars in MW & LMC (Leitherer+, 2019)
He II emission from Wolf-Rayet stars as a tool for measuring dust reddening.
Leitherer C., Lee J.C., Faisst A.
<Astron. J., 158, 192-192 (2019)>
=2019AJ....158..192L 2019AJ....158..192L (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Magellanic Clouds ; Stars, Wolf-Rayet ;
Interstellar medium ; Spectral types ; Equivalent widths ;
Spectra, ultraviolet ; Spectra, optical ; Reddening
Keywords: Wolf-Rayet stars - Interstellar dust extinction -
Interstellar medium - Stellar populations - Young star clusters -
Starburst galaxies
Abstract:
We calibrated a technique to measure dust attenuation in star-forming
galaxies. The technique utilizes the stellar-wind lines in Wolf-Rayet
stars, which are widely observed in galaxy spectra. The He II 1640 and
4686 features are recombination lines whose ratio is largely determined
by atomic physics. Therefore they can serve as a stellar dust probe in
the same way as the Balmer lines are used as a nebular probe. We measured
the strength of the He II 1640 line in 97 Wolf-Rayet stars in the Galaxy
and the Large Magellanic Cloud. The reddening corrected fluxes follow
a tight correlation with a fixed ratio of 7.76 for the He II 1640 to 4686
line ratio. Dust attenuation decreases this ratio. We provide a relation
between the stellar E(B-V) and the observed line ratio for several
attenuation laws. Combining this technique with the use of the nebular
Balmer decrement allows the determination of the stellar and nebular dust
attenuation in galaxies and can probe its effects at different stellar age
and mass regimes, independently of the initial mass function and the star
formation history. We derived the dust reddening from the He II line fluxes
and compared it to the reddening from the Balmer decrement and from the
slope of the ultraviolet continuum in two star-forming galaxies. The three
methods result in dust attenuations which agree to within the errors.
Future application of this technique permits studies of the stellar dust
attenuation compared to the nebular attenuation in a representative
galaxy sample.
Description:
All available spectra of the 97 W-R stars listed in Tables 1 and 2
were retrived from the Mikulski Archive for Space Telescopes (MAST).
The spectra were obtained with IUE's SWP camera in the low-dispersion
mode at a resolution of approximately 6Å. The 10"x20" entrance
aperture was used for all considered spectra in order to maximize the
photometric accuracy. Instrumental details of the IUE satellite and
its spectrograph can be found in Boggess et al. (1978Natur.275..377B 1978Natur.275..377B
1978Natur.275..377B 1978Natur.275..377B, 1978Natur.275...37I 1978Natur.275...37I 1978Natur.275...37I 1978Natur.275...37I).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 77 45 Milky Way program stars
table2.dat 77 52 LMC program stars
table3.dat 53 97 Optical data for all program stars
table4.dat 35 89 Reddening-free He II line fluxes
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See also:
III/143 : Spectrophotometry of Wolf-Rayet Stars (Torres-Dodgen+ 1988)
III/215 : 7th Catalog of Galactic Wolf-Rayet stars (van der Hucht, 2001)
J/A+AS/108/669 : IUE spectra of WR stars (Niedzielski+, 1994)
J/A+A/565/A27 : Wolf-Rayet stars in Large Magellanic Cloud (Hainich+, 2014)
J/MNRAS/452/2858 : NIR spectroscopy of Galactic WR stars. III (Kanarek+, 2015)
J/ApJ/863/181 : The fifth catalog of LMC Wolf-Rayet stars (Neugent+, 2018)
Byte-by-byte Description of file: table[12].dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- WR W-R identifier (WR NNN or WR NNa) (1)
11- 21 A11 --- OName Alternative designation
23- 24 I2 h RAh Hour of Right Ascension (J2000) (2)
26- 27 I2 min RAm Minute of Right Ascension (J2000) (2)
29- 33 F5.2 s RAs Second of Right Ascension (J2000) (2)
35 A1 --- DE- Sign of the Declination (J2000) (2)
36- 37 I2 deg DEd Degree of Declination (J2000) (2)
39- 40 I2 arcmin DEm Arcminute of Declination (J2000) (2)
42- 45 F4.1 arcsec DEs Arcsecond of Declination (J2000) (2)
47- 56 A10 --- SpType Spectral type (1)
58- 65 A8 --- IUE Identifier of the IUE spectrum (SWPNNNNN)
67- 70 F4.2 [0.1nm] log(EW(1640)) [0.28/2.16] Measured equivalent width of
He II 1640 (Å)
72- 77 F6.2 [mW/m2] log(F(1640)) [-12.89/-7.78] Measured line flux of
He II 1640 (in erg/s/cm2)
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Note (1): From van der Hucht (2001, Cat. III/215) in Table 1 and from
Breysacher et al. (1999A&AS..137..117B 1999A&AS..137..117B) in Table 2.
Note (2): The coordinates are from van der Hucht (2001, Cat. III/215) in Table 1
and from Breysacher et al. (1999A&AS..137..117B 1999A&AS..137..117B) in Table 2 and may be
different from the MAST coordinates.
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 A9 --- WR W-R identifier from van der Hucht (2001,
Cat. III/215) or Breysacher et al.
(1999A&AS..137..117B 1999A&AS..137..117B)
11- 15 F5.2 [0.1nm] log(EW(4686)) [-0.3/2.69] Published equivalent width
of He II 4686 (Å)
17- 22 F6.2 [mW/m2] log(F(4686)) [-12.85/-8.68]? Published line flux of
He II 4686 (in erg/s/cm2)
24- 31 A8 --- Ref(4686) Reference for the 4686 data (1)
33- 37 F5.2 mag vmag [6.44/16.22] Published v magnitude
39- 43 F5.2 mag (b-v) [-0.25/0.93] Published (b-v) color
45- 46 I2 --- r_(b-v) [12/14] Reference for (b-v) (2)
48- 53 F6.2 [mW/m2] log(Fc(4686)) [-13.38/-8.59] Calculated line flux of
He II 4686 (in erg/s/cm2)
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Note (1): Reference as follows:
1 = Conti & Morris (1990AJ.....99..898C 1990AJ.....99..898C);
2 = Smith et al. (1996MNRAS.281..163S 1996MNRAS.281..163S);
3 = Conti & Massey (1989ApJ...337..251C 1989ApJ...337..251C);
4 = Crowther et al. (1995A&A...293..427C 1995A&A...293..427C);
5 = Crowther & Hadfield (2006A&A...449..711C 2006A&A...449..711C);
6 = P. Crowther (2019, private communication);
7 = Schnurr et al. (2008MNRAS.389..806S 2008MNRAS.389..806S);
8 = Crowther et al. (1995A&A...293..172C 1995A&A...293..172C);
9 = Foellmi et al. (2003MNRAS.338.1025F 2003MNRAS.338.1025F);
10 = Torres-Dodgen & Massey (1988, Cat. III/143);
11 = Crowther & Smith (1997A&A...320..500C 1997A&A...320..500C).
Note (2): Reference as follows:
12 = van der Hucht (2001, Cat. III/215);
13 = Breysacher et al. (1999A&AS..137..117B 1999A&AS..137..117B);
14 = Calculated from (B-V).
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 A9 --- WR W-R identifier from van der Hucht (2001,
Cat. III/215) or Breysacher et al.
(1999A&AS..137..117B 1999A&AS..137..117B)
11- 14 F4.2 mag E(b-v) [0.06/1.22] Published reddening from
continuum fitting
16 I1 --- r_E(b-v) [1/4] Reference for the reddening data
(1)
18- 23 F6.2 [mW/m2] log(F0(1640)) [-12.54/-7.3] Dereddened He II 1640 line
flux (in erg/s/cm2)
25- 30 F6.2 [mW/m2] log(F0(4686)) [-12.88/-8.06] Dereddened He II 4686
line flux (in erg/s/cm2)
32- 35 F4.2 [-] logR0 [0.24/2.16] Logarithmic ratio of
the 1640/4686 flux
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Note (1): Reference as follows:
1 = Hamann et al. (2006A&A...457.1015H 2006A&A...457.1015H);
2 = Schmutz & Vacca (1991A&AS...89..259S 1991A&AS...89..259S);
3 = Crowther & Dessart (1998MNRAS.296..622C 1998MNRAS.296..622C);
4 = Hainich et al. (2014, J/A+A/565/A27).
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(End) Tiphaine Pouvreau [CDS] 13-Jan-2020