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 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 2004ApJS..154..359B).
i = Published previously in Watson et al. (2004ApJS..154..391W 2004ApJS..154..391W).
j = Published previously in Boogert et al. (2000A&A...360..683B 2000A&A...360..683B).
k = Published previously in Pontoppidan et al. (2005ApJ...622..463P 2005ApJ...622..463P).
l = Published previously in Keane et al. (2001A&A...376..254K 2001A&A...376..254K).
m = Published previously in Knez et al. (2005ApJ...635L.145K 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 H2O 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 ? NH4+ 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 1999A&A...342L..32D) (CH3OH),
b = Boogert et al. (2000A&A...360..683B 2000A&A...360..683B) (CH3OH),
o = Boogert et al. (2004ApJS..154..359B 2004ApJS..154..359B) (H2O and CH3OH),
r = Brooke et al. (1999ApJ...517..883B 1999ApJ...517..883B) (H2O),
e = Eiroa & Hodapp (1989A&A...210..345E 1989A&A...210..345E) (H2O),
k = Keane et al. (2001A&A...376..254K 2001A&A...376..254K) (H2O),
n = Knez et al. (2005ApJ...635L.145K 2005ApJ...635L.145K) (H2O and CH3OH),
p = Pontoppidan et al. (2004A&A...426..925P 2004A&A...426..925P) (H2O and CH3OH),
t = Pontoppidan et al. (2005ApJ...622..463P 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 2003A&A...398.1049S).
--------------------------------------------------------------------------------
History:
From electronic version of the journal
References:
Pontoppidan et al. 2008ApJ...678.1005P 2008ApJ...678.1005P. Paper II.
Oberg et al. 2008ApJ...678.1032O 2008ApJ...678.1032O. Paper III.
Bottinelli et al. 2010ApJ...718.1100B 2010ApJ...718.1100B. Paper IV.
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 20-Sep-2010