J/ApJ/693/L81 Extinction in star-forming regions (McClure, 2009)
Observational 5-20 µm interstellar extinction curves toward star-forming
regions derived from Spitzer IRS spectra.
McClure M.
<Astrophys. J., 693, L81-L85 (2009)>
=2009ApJ...693L..81M 2009ApJ...693L..81M
ADC_Keywords: Molecular clouds ; Extinction ; Infrared sources ; Stars, dwarfs
Keywords: infrared: stars - ISM: clouds - stars: formation
Abstract:
Using Spitzer Infrared Spectrograph observations of G0-M4III stars
behind dark clouds, I construct 5-20um empirical extinction curves for
0.3≤AK<7, which is equivalent to AV between ∼3 and 50. For
AK<1, the curve appears similar to the Mathis diffuse interstellar
medium extinction curve, but with a greater degree of extinction. For
AK>1, the curve exhibits lower contrast between the silicate and
absorption continuum, develops ice absorption, and lies closer to the
Weingartner and Draine RV=5.5 Case B curve, a result which is
consistent with that of Flaherty et al. (2007ApJ...663.1069F 2007ApJ...663.1069F) and
Chiar et al. (2007ApJ...666L..73C 2007ApJ...666L..73C). Recently, work using Spitzer
Infrared Array Camera data by Chapman et al. independently reaches a
similar conclusion that the shape of the extinction curve changes as a
function of increasing AK. By calculating the optical depths of the
9.7um silicate and 6.0, 6.8, and 15.2um ice features, I determine that
a process involving ice is responsible for the changing shape of the
extinction curve and speculate that this process is a coagulation of
ice-mantled grains rather than ice-mantled grains alone.
Description:
I began my analysis with 28 of the G0-M4III stars discussed in Chiar
et al., 2007ApJ...666L..73C 2007ApJ...666L..73C, that lie behind the Taurus, Chameleon I,
Serpens, Barnard 59, Barnard 68, and IC 5146 molecular clouds. Most of
these have been observed with the Spitzer IRS. The sample is given in
table 1, with the AOR numbers.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 114 34 Spectral type information for the entire sample
table2.dat 24 1532 Final, composite extinction curves
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See also:
J/ApJ/663/320 : IR-through-UV extinction curve (Fitzpatrick+, 2007)
J/A+AS/111/57 : Synthetic absorption in star forming regions (Olofsson, 1995)
J/A+A/275/549 : Interstellar extinction curves (Jenniskens+ 1993)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Cld Cloud name
12- 31 A20 --- Name Star name
32 A1 --- r_Name [b] Flag on Name (1)
34- 49 A16 --- 2MASSJ 2MASS designation (HHMMSSss+DDMMSSs)
51- 55 A5 --- SpT MK spectral type
56 A1 --- r_SpT [c] Flag on SpT (2)
58- 62 I5 --- PID AOR number (Astronomical Observation Request
identification number)
64 A1 --- l_AK Limit flag on AK
65- 68 F4.2 --- AK ? K-band extinction (3)
70- 73 F4.2 --- e_AK ? AK uncertainty
75- 78 F4.2 --- tau9.7 ? Optical depth of the 9.7um silicate
80- 83 F4.2 --- e_tau9.7 ? tau9.7 uncertainty
85- 88 F4.2 --- tauH2O ? Optical depth of the 6um (H2O ice)
90- 93 F4.2 --- e_tauH2O ? tauH2O uncertainty
95- 98 F4.2 --- tauMet ? Optical depth of the 6.8um ("methanol" ice)
100-103 F4.2 --- e_tauMet ? tauMet uncertainty
105-109 F5.2 --- tauCO2 ? Optical depth of the 15.2um (CO2 ice)
111-114 F4.2 --- e_tauCO2 ? tauCO2 uncertainty
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Note (1): b = Object from Shenoy et al. (2008, Cat. J/ApJS/176/457).
Note (2): c = SpT from Knez et al. (2005ApJ...635L.145K 2005ApJ...635L.145K).
Note (3): The conversion factor from AKto AV, assuming the total to
selective ab soption ratio RV=5.0, is AV/AK=7.75.
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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- 8 F8.2 um lambda Wavelength (1)
10- 16 E7.3 --- Al/AK1 Aλ/AKs for 0.3<Ak<1
18- 24 E7.3 --- Al/AK2 Aλ/AKs for 1<Ak<7
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Note (1): These curves are composites of:
[0.3,2.3]um = Mathis (1990ARA&A..28...37M 1990ARA&A..28...37M) RV=5.0
[3.6,4.5]um = Flaherty et al. (2007ApJ...663.1069F 2007ApJ...663.1069F)
[5.19,17(or 30)]um = This work
[17(or30),10000]um = Weingartner & Draine (2001ApJ...548..296W 2001ApJ...548..296W) RV=5.5
Case B scaled. Refer to Section 3.1 for clarification and more details.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 08-Mar-2011