J/ApJ/678/985 c2d Spitzer survey of interstellar ices. I. (Boogert+, 2008)
The c2d Spitzer spectroscopic survey of ices around low-mass young stellar objects. I. H2O and the 5-8µm Bands. Boogert A.C.A., Pontoppidan K.M., Knez C., Lahuis F., Kessler-Silacci J., Van Dishoeck E.F., Blake G.A., Augereau J.-C., Bisschop S.E., Bottinelli S., Brooke T.Y., Brown J., Crapsi A., Evans N.J.II, Fraser H.J., Geers V., Huard T.L., Jorgensen J.K., Oberg K.I., Allen L.E., Harvey P.M., Koerner D.W., Mundy L.G., Padgett D.L., Sargent A.I., Stapelfeldt K.R. <Astrophys. J., 678, 985-1004 (2008)> =2008ApJ...678..985B
ADC_Keywords: YSOs ; Spectra, infrared ; Abundances Keywords: astrochemistry - infrared: ISM - infrared: stars - ISM: abundances - ISM: molecules - stars: formation Abstract: To study the physical and chemical evolution of ices in solar-mass systems, a spectral survey is conducted of a sample of 41 low-luminosity YSOs (L∼0.1-10L☉) using 3-38um Spitzer and ground-based spectra. The sample is complemented with previously published Spitzer spectra of background stars and with ISO spectra of well-studied massive YSOs (L∼105L☉). The long-known 6.0 and 6.85um bands are detected toward all sources, with the Class 0-type YSOs showing the deepest bands ever observed. The 6.0um band is often deeper than expected from the bending mode of pure solid H2O. The additional 5-7um absorption consists of five independent components, which, by comparison to laboratory studies, must be from at least eight different carriers. Much of this absorption is due to simple species likely formed by grain surface chemistry, at abundances of 1%-30% for CH3OH, 3%-8% for NH3, 1%-5% for HCOOH, ∼6% for H2CO, and ∼0.3% for HCOO- relative to solid H2O. The 6.85um band has one or two carriers, of which one may be less volatile than H2O. Its carrier(s) formed early in the molecular cloud evolution and do not survive in the diffuse ISM. If an NH4+ -containing salt is the carrier, its abundance relative to solid H2O is ∼7%, demonstrating the efficiency of low-temperature acid-base chemistry or cosmic-ray-induced reactions. Possible origins are discussed for enigmatic, very broad absorption between 5 and 8um. Finally, the same ices are observed toward massive and low-mass YSOs, indicating that processing by internal UV radiation fields is a minor factor in their early chemical evolution. Description: The source sample is selected based on the presence of ice absorption features and consists of a combination of known low-mass YSOs and new ones identified from their Spitzer IRAC and MIPS broadband spectral energy distributions. Spitzer IRS spectra were obtained as part of the c2d Legacy program (PIDs 172 and 179), as well as a dedicated open time program (PID 20604). File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 121 51 Source sample table2.dat 111 51 Fit parameters table3.dat 71 51 Column densities of the ices
See also: J/ApJS/86/713 : IR spectroscopy of ices (Hudgins+, 1993) Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 23 A23 --- Name Source name 24- 26 A3 --- r_Name [h-m ] Previous reference (1) 28- 42 A15 --- OName Alias 44- 45 I2 h RAh Hour of right ascension (J2000) (2) 47- 48 I2 min RAm Minute of right ascension (J2000) (2) 50- 54 F5.2 s RAs Second of right ascension (J2000) (2) 56 A1 --- DE- Declination sign (J2000) (2) 57- 58 I2 deg DEd Degree of declination (J2000) (2) 60- 61 I2 arcmin DEm Arcminute of declination (J2000) (2) 63- 66 F4.1 arcsec DEs Arcsecond of declination (J2000) (2) 68- 74 A7 --- CloudID Name of cloud 76- 79 A4 --- type Source type (3) 81- 85 F5.2 --- alpha ?=- Brodband α spectral index (4) 86 A1 --- f_alpha [g] Remarks on alpha (5) 88- 97 A10 --- ObsID Key for Spitzer of ISO observations (6) 99-113 A15 --- Module Spitzer IRS modules used (7) 115-121 A7 --- Lband Complementary observations in L-band (8)
Note (1): Previous references as follows: h = Published previously in Boogert et al. (2004ApJS..154..359B). i = Published previously in Watson et al. (2004ApJS..154..391W). j = Published previously in Boogert et al. (2000A&A...360..683B). k = Published previously in Pontoppidan et al. (2005ApJ...622..463P). l = Published previously in Keane et al. (2001A&A...376..254K). m = Published previously in Knez et al. (2005ApJ...635L.145K). Note (2): Position used in Spitzer IRS observations. Note (3): Source type as follows: Low = low mass YSO; High = massive YSO; bg = background star. Note (4): Broadband spectral index as defined in eq. (1), in section 2. Note (5): g = Spectral index α enhanced due to foreground extinction. Exclusion of Ks band flux gives much lower α: -0.16 (Elias 29), -0.02 (B5 IRS 1), 0.18 (B5 IRS 3), and 0.38 (EC 82). Note (6): AOR key for Spitzer and TDT number for ISO observations. Note (7): Spitzer IRS modules used: SL = Short-Low (5-14um, R∼100), LL = Long-Low (14-34um, R∼100), SH = Short-High (10-20um, R∼600), LH = Long-High (20-34um, R∼600); ISO SWS modes used (2.3-40um): SWS01 speed 1 (R∼250), speed 2 (R∼250), speed 3 (R∼400), speed 4 (R∼800). Note (8): Complementary ground-based L-band observations: Keck NIRSPEC or VLT ISAAC.
Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 23 A23 --- Name Source name 25- 27 I3 K T The H_2_O temperature (1) 29 A1 --- q_T [*] most accurate temperature (2) 31 A1 --- l_E6 Limit flag on E6 32- 36 F5.2 --- E6 The 6 micron excess; as defined in Eq. 2 38- 41 F4.2 --- e_E6 ? Statistical error in E6 (3) 43- 46 F4.2 --- tau9.7 ? Peak optical depth at 9.7 microns (4) 48- 51 F4.2 --- e_tau9.7 ? Statistical error in tau9.7 (5) 53- 56 F4.2 --- tau6 Peak optical depth at 6.0 microns (6) 58- 61 F4.2 --- e_tau6 Statistical error in tau6.0 63- 66 F4.2 --- tauC1 Peak optical depth component C1 68- 71 F4.2 --- e_tauC1 Statistical error in tauC1 73- 76 F4.2 --- tauC2 Peak optical depth component C2 78- 81 F4.2 --- e_tauC2 Statistical error in tauC2 83- 86 F4.2 --- tauC3 Peak optical depth component C3 88- 91 F4.2 --- e_tauC3 Statistical error in tauC3 93- 96 F4.2 --- tauC4 Peak optical depth component C4 98-101 F4.2 --- e_tauC4 Statistical error in tauC4 103-106 F4.2 --- tauC5 Peak optical depth component C5 108-111 F4.2 --- e_tauC5 Statistical error in tauC5 (7)
Note (1): Pure H2O laboratory ice (Hudgins et al. 1993, Cat. J/ApJS/86/713) assumed. Note (2): the asterisk (*) indicates most accurate value because of the availability of good quality L-band spectra. Note (3): Statistical error includes uncertainty in N(H2O). Note (4): Without correction for underlying emission. Blank values indicate emission. Note (5): Statistical error includes 10% of τ9.7 to account for errors in the continuum determination. Note (6): including H2O absorption. Note (7): Statistical error includes uncertainty in N(H2O) as this affects the baseline level. The continuum uncertainty is not included. It is likely on the order of 0.03 for most sources.
Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
1- 23 A23 --- Name Source name 24- 26 A3 --- Ref [a-t, ] Reference(s) for column density values (1) 28 A1 --- l_NH2O Limit flag on NH20 (2) 29- 33 F5.2 10+18/cm2 NH2O H20 column density 35- 38 F4.2 10+18/cm2 e_NH2O ? NH20 uncertainty 40 A1 --- f_NH2O [c] Flag on NH20 (3) 42- 43 A2 --- l_NHCOOH [≤ ] Limit flag on NHCOOH (2) 44- 47 F4.1 % NHCOOH ? HCOOH column density in percentage of H2O (4) 49- 51 F3.1 % e_NHCOOH ? NHCOOH uncertainty 53 A1 --- l_NCH3OH Limit flag on NCH3OH (2) 54- 57 F4.1 % NCH3OH ? CH3OH column density in percentage of H2O 59- 61 F3.1 % e_NCH3OH ? NCH3OH uncertainty 62 A1 --- f_NCH3OH [d] Flag on NCH3OH (5) 64- 67 F4.1 % NNH4 ? NH_4_^+^ column density in percentage of H2O (6) 69- 71 F3.1 % e_NNH4 ? NNH4 uncertainty
Note (1): Value obtained from or comparable to previous work or references therein as follows: a = Dartois et al. (1999A&A...342L..32D) (CH3OH), b = Boogert et al. (2000A&A...360..683B) (CH3OH), o = Boogert et al. (2004ApJS..154..359B) (H2O and CH3OH), r = Brooke et al. (1999ApJ...517..883B) (H2O), e = Eiroa & Hodapp (1989A&A...210..345E) (H2O), k = Keane et al. (2001A&A...376..254K) (H2O), n = Knez et al. (2005ApJ...635L.145K) (H2O and CH3OH), p = Pontoppidan et al. (2004A&A...426..925P) (H2O and CH3OH), t = Pontoppidan et al. (2005ApJ...622..463P) (H2O and CH3OH). Note (2): Upper limits are of 3σ significance. Note (3): The 13um H2O libration mode used for N(H2O) determination (3um band in other cases). Note (4): Detections and 3σ upper limits of N(HCOOH) based on the 7.25um C-H deformation mode. Sources for which the 5.85um C=O stretching mode provides tighter constraints are indicated with "≤". Note (5): The 3.53um band provides a better or comparable constraint to N(CH3OH) than does the 9.7um band. Note (6): Assuming that both C3 and C4 components are due to NH4+, which is still a matter of debate (Sect. 6.1); integrated band strength A=4.4x10-17cm/molecule assumed (Schutte & Khanna, 2003A&A...398.1049S).
History: From electronic version of the journal References: Pontoppidan et al. 2008ApJ...678.1005P. Paper II. Oberg et al. 2008ApJ...678.1032O. Paper III. Bottinelli et al. 2010ApJ...718.1100B. Paper IV.
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 20-Sep-2010
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