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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
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) and Chiar et al. (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, 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:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 114 34 Spectral type information for the entire sample table2.dat 24 1532 Final, composite extinction curves
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
Bytes Format Units Label Explanations
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
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). Note (3): The conversion factor from AKto AV, assuming the total to selective ab soption ratio RV=5.0, is AV/AK=7.75.
Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
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
Note (1): These curves are composites of: [0.3,2.3]um = Mathis (1990ARA&A..28...37M) RV=5.0 [3.6,4.5]um = Flaherty et al. (2007ApJ...663.1069F) [5.19,17(or 30)]um = This work [17(or30),10000]um = Weingartner & Draine (2001ApJ...548..296W) RV=5.5 Case B scaled. Refer to Section 3.1 for clarification and more details.
History: From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 08-Mar-2011
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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