J/ApJ/764/25 FUSE spectra analysis of hot subdwarf stars (Jenkins, 2013)
The fractional ionization of the warm neutral interstellar medium.
Jenkins E.B.
<Astrophys. J., 764, 25 (2013)>
=2013ApJ...764...25J 2013ApJ...764...25J
ADC_Keywords: Equivalent widths ; Spectra, ultraviolet ; Interstellar medium ;
Stars, subdwarf
Keywords: ISM: atoms; ISM: general; ISM: lines and bands;
local interstellar matter; techniques: spectroscopic
Abstract:
When the neutral interstellar medium is exposed to extreme-ultraviolet
and soft X-ray radiation, the argon atoms in it are far more
susceptible to being ionized than the hydrogen atoms. We make use of
this fact to determine the level of ionization in the nearby warm
neutral medium. By analyzing Far-Ultraviolet Spectroscopic Explorer
observations of ultraviolet spectra of 44 hot subdwarf stars a few
hundred parsecs away from the Sun, we can compare column densities of
Ar I to those of O I, where the relative ionization of oxygen can be
used as a proxy for that of hydrogen. The measured deficiency
[ArI/OI]=-0.427±0.11dex below the expectation for a fully neutral
medium implies that the electron density n(e)~0.04/cm3 if
n(H)=0.5/cm3. This amount of ionization is considerably larger than
what we expect from primary photoionizations resulting from cosmic
rays, the diffuse X-ray background, and X-ray emitting sources within
the medium, along with the additional ionizations caused by energetic
secondary photoelectrons, Auger electrons, and photons from helium
recombinations. We favor an explanation that bursts of radiation
created by previous, nearby supernova remnants that have faded by now
may have elevated the ionization, and the gas has not yet recombined
to a quiescent level. A different alternative is that the low-energy
portion of the soft X-ray background is poorly shielded by the H I
because it is frothy and has internal pockets of very hot, X-ray
emitting gases.
Description:
We selected calibrated FUSE data from MAST for stars classified as sdO
and sdB spectral types. For every target, two combined spectra were
created: one was made up with shifts appropriate to the spectral
region covering the ArI line at 1048Å, while the other had
differentials that were optimized for the wavelengths that covered the
weakest OI lines near 920Å (see section 3 for further details).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 132 44 Equivalent widths measured from FUSE spectra
table2.dat 76 44 Results for [ArI/OI]
fig6.dat 63 1785 *Figure 6 data used for the figure
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Note on fig6.dat : synthesis of the sum of the extragalactic power-law
emission and transabsorption emission (TAE) synthesis.
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See also:
VI/129 : The FUSE Observation Log (FUSE, 1999-2007)
J/AJ/141/50 : White-light flares on Kepler cool stars (Walkowicz+, 2011)
J/A+A/533/A62 : Atomic Data for Neutron-Capture Elements. II (Sterling, 2011)
J/ApJ/734/65 : CI radial velocities with HST/STIS (Jenkins+, 2011)
J/ApJ/711/1236 : Equivalent width of H2 from FUSE (Jensen+, 2010)
J/A+A/510/A54 : NaI and CaII interstellar absorption (Welsh+, 2010)
J/ApJ/700/1299 : Gas-phase element depletions in the ISM (Jenkins, 2009)
J/ApJS/176/59 : FUSE survey of OVI in the disk of the Milky Way (Bowen+, 2008)
J/ApJ/647/328 : FUSE survey of OVI in ISM (Dixon+, 2006)
J/ApJ/647/312 : FUSE survey of OVI in the Milky Way (Otte+, 2006)
J/ApJS/163/282 : Molecular hydrogen column densities (Wakker+, 2006)
J/ApJS/163/207 : Oscillator and collision strengths in NI (Tayal+, 2006)
J/ApJS/147/61 : Interstellar Ca I absorption (Welty+, 2003)
J/ApJS/146/1 : O VI absorption in FUSE survey (Wakker+, 2003)
J/A+A/346/785 : NaI in Local Bubble (Sfeir+, 1999)
J/A+AS/125/149 : CHIANTI: An Atomic Database For Emission Lines I. (Dere+ 1997)
J/A+AS/123/159 : IRON Project. XXII. C and O radiative rates (Galavis+ 1997)
J/A+AS/109/125 : Photoionisation cross section (Verner+, 1995)
J/A+AS/97/443 : Fluorescence for Be to Zn (Kaastra+ 1993)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 21 A21 --- Name Star name
22 A1 --- n_Name [def] Other star identifications in the note (1)
24- 26 I3 0.1pm W1048 [-21/179] Equivalent width for ArI 1048.220 line
log(fλ)=2.440 in mÅ (2)
28- 29 I2 0.1pm e_W1048 [3/27] W1048 uncertainty
31 A1 --- f_W919 [(] (: W919 not used in the linear fit
33- 34 I2 0.1pm W919 [-3/58]? Equivalent width for OI 919.917 line
log(fλ)=-0.788, ew6=11.6 in mÅ (2)
36- 37 I2 0.1pm e_W919 [3/39]? W919 uncertainty
39 A1 --- f_W922 [(] (: W922 not used in the linear fit
41- 42 I2 0.1pm W922 [-4/86]? Equivalent width for OI 922.200 line
log(fλ)=-0.645, ew6=15.3 in mÅ (2)
44- 45 I2 0.1pm e_W922 [5/31]? W922 uncertainty
47 A1 --- f_W925 [(] (: W925 not used in the linear fit
49- 51 I3 0.1pm W925 [13/107] Equivalent width for OI 925.446 line
log(fλ)=-0.484, ew6=20.6 in mÅ (2)
53- 54 I2 0.1pm e_W925 [3/39] W925 uncertainty
56 A1 --- f_W916 [(] (: W916 not used in the linear fit
58- 60 I3 0.1pm W916 [25/101]? Equivalent width for OI 916.815 line
log(fλ)=-0.362, ew6=25.0 in mÅ (2)
62- 63 I2 0.1pm e_W916 [4/38]? W916 uncertainty
65 A1 --- f_W930 [(] (: W930 not used in the linear fit
67- 69 I3 0.1pm W930 [20/134]? Equivalent width for OI 930.257 line
log(fλ)=-0.301, ew6=27.8 in mÅ (2)
71- 72 I2 0.1pm e_W930 [4/59]? W930 uncertainty
74- 75 I2 0.1pm W920 [-2/99]? Equivalent width for OI 919.658 line
log(fλ)=-0.137, ew6=34.5 in mÅ (2)
77- 78 I2 0.1pm e_W920 [4/46]? W920 uncertainty
80 A1 --- f_W921 [(] (: W921 not used in the linear fit
82- 84 I3 0.1pm W921 [30/166]? Equivalent width for OI 921.857 line
log(fλ)=-0.001, ew6=40.4 in mÅ (2)
86- 87 I2 0.1pm e_W921 [4/34]? W921 uncertainty
89 A1 --- f_W924 [(] (: W924 not used in the linear fit
91- 93 I3 0.1pm W924 [15/152] Equivalent width for OI 924.950 line
log(fλ)=0.155, ew6=46.9 in mÅ (2)
95- 96 I2 0.1pm e_W924 [3/38] W924 uncertainty
98 A1 --- f_W950 [(] (: W950 not used in the linear fit
100-102 I3 0.1pm W950 [28/175]? Equivalent width for OI 950.885 line
log(fλ)=0.176, ew6=49.0 in mÅ (2)
104-105 I2 0.1pm e_W950 [3/38]? W950 uncertainty
107 A1 --- f_W976 [(] (: W976 not used in the linear fit
109-111 I3 0.1pm W976 [41/256]? Equivalent width for OI 976.448 line
log(fλ)=0.509 in mÅ (2)
113-114 I2 0.1pm e_W976 [4/39]? W976 uncertainty
116 A1 --- f_W948 [(] (: W948 not used in the linear fit
118-120 I3 0.1pm W948 [68/180]? Equivalent width for OI 948.686 line
log(fλ)=0.778 in mÅ (2)
122-123 I2 0.1pm e_W948 [4/22]? W948 uncertainty
125 A1 --- f_W971 [(] (: W971 not used in the linear fit
127-129 I3 0.1pm W971 [62/228]? Equivalent width for OI 971.738 line
log(fλ)=1.052 in mÅ (2)
131-132 I2 0.1pm e_W971 [3/39]? W971 uncertainty
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Note (1): Flag as follows:
d = Name recognized by SIMBAD: 2MASS J20515997-4042465.
e = Central star of the planetary nebula NGC 6905.
f = Name recognized by SIMBAD: 2MASS J09070812-0306139.
Note (2): Wavelengths are in Å, line strengths in terms of
log(fλ) are taken from Morton (2003ApJS..149..205M 2003ApJS..149..205M), and ew6
are the equivalent width in mÅ for N(OI)=1016/cm2 and b=6km/s.
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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- 21 A21 --- Name Star Name
23- 28 F6.2 deg GLON SIMBAD Galactic longitude
30- 35 F6.2 deg GLAT SIMBAD Galactic latitude
37- 41 F5.2 mag Bmag [9.3/16.3]? SIMBAD B-band magnitude
43- 47 F5.2 mag Vmag [9.6/15.2]? SIMBAD V-band magnitude
49- 53 F5.2 [Sun] b_[ArI/OI] [-3.8/-0.01] Lower limit of [ArI/OI] (3)
55- 59 F5.2 [Sun] [ArI/OI] [-1.9/0.3] Best value of [ArI/OI] (3)
61- 65 F5.2 [Sun] B_[ArI/OI] [-1/0.7] Upper limit of [ArI/OI] (3)
67- 71 F5.2 --- Err [2.2/11.1] Denominator (c1) Value/Error (4)
73- 76 F4.2 --- Prob [0.01/1] Probability of worse fit
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Note (3): [ArI/OI]=(N(ArI)/N(OI)/(Ar/O)☉). The range of possible values
shown here does not include an overall systematic error that arises
from the uncertainties in the constants that are included in
Equation (1), which amounts to a combined error of 0.11dex.
Note (4): The relevance of this quantity is discussed in the text that follows
Equation (4). If the listed value is less than about 3, the positive
value of the error quotient may be misleading.
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Byte-by-byte Description of file: fig6.dat
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Bytes Format Units Label Explanations
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1- 8 F8.2 eV E [24/3995] Photon energy
9- 19 E11.3 ph/cm2/s obs [69/281900] External observed background
(4πE.F(obs)) (upper panel)
20- 30 E11.3 ph/cm2/s SNR [0.09/215900] External flux from supernova
remnant(s) (4πE.F(SNR)) (upper panel)
31- 41 E11.3 ph/cm3/s E.F(MS) Internal flux for the injection of ionizing
photons from main sequence stars
42- 52 E11.3 ph/cm3/s E.F(AB) Internal flux for the injection of ionizing
photons from active binaries
53- 63 E11.3 ph/cm3/s E.F(WD) Internal flux for the injection of ionizing
photons from white dwarfs
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 23-Oct-2014