J/ApJ/704/606 Protostars in the Vela Molecular Cloud (Giannini+, 2009)
Pre-main sequence variables in the VMR-D: identification of T Tauri-like
accreting protostars through Spitzer-IRAC variability.
Giannini T., Lorenzetti D., Elia D., Strafella F., De Luca M., Fazio G.,
Marengo M., Nisini B., Smith H.A.
<Astrophys. J., 704, 606-617 (2009)>
=2009ApJ...704..606G 2009ApJ...704..606G
ADC_Keywords: Molecular clouds ; YSOs ; Photometry, infrared
Keywords: catalogs - infrared: ISM - infrared: stars - stars: formation -
stars: pre-main sequence - stars: variables: other
Abstract:
We present a study of the infrared variability of young stellar
objects by means of two Spitzer-IRAC images of the Vela Molecular
Cloud D (VMR-D) obtained in observations separated in time by about
six months. By using the same space-born IR instrumentation, this
study eliminates all the unwanted effects due to differences in
sensitivity, confusion, saturation, calibration, and filter
bandpasses, issues that are usually unavoidable when comparing
catalogs obtained from different instruments. The VMR-D map covers
about 1.5deg2 of a site where star formation is actively ongoing. We
are interested in accreting pre-main sequence variables whose
luminosity variations are due to intermittent events of disk accretion
(i.e., active T Tauri stars and EXor-type objects). The variable
objects have been selected from a catalog of more than 170000 sources
detected at an S/N≥5 (Cat. J/ApJ/719/9). We then searched the sample
of variables for ones whose photometric properties such as IR excess,
color-magnitude relationships, and spectral energy distribution, are
as close as possible to those of known EXor's. Indeed, the latter are
monitored in a more systematic way than T Tauri stars and the
mechanisms that regulate the observed phenomenology are exactly the
same. Hence, the modalities of the EXor behavior are adopted as
driving criterion for selecting variables in general. We ultimately
selected 19 bona fide candidates that constitute a well defined sample
of new variable targets for further investigation (monitoring,
spectroscopy). Out of these, 10 sources present a Spitzer MIPS 24um
counterpart, and have been classified as three Class I, five flat
spectrum, and two Class II objects, while the spectral energy
distribution of the other nine sources is compatible with evolutionary
phases older than Class I.
Description:
In this paper, we make use of a map of approximately 1.5deg2 of the
VMC-D that we obtained with Spitzer-IRAC Cycle-3 GTO (PID: 30335; PI:
G.Fazio) at 3.6, 4.5, 5.8, and 8.0um. Observations were carried out
in two separate AORs on 2007 February 21 UT and 2007 July 4 UT (AOR
Keys: 17606656 and 17606912, respectively) by adopting half-array
cross scan offsets.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 75 94 Magnitudes of the 47 selected variables at the
2 epochs (2007-02-21 and 2007-07-04)
table3.dat 37 47 Coded photometric properties of the selected sources
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See also:
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
J/ApJ/719/9 : Pre-main sequence variables in the VMR-D (Strafella+, 2010)
J/ApJ/671/470 : MIPS survey of YSOs in Vela Molecular Ridge-D (Giannini+,
2007)
J/A+AS/136/471 : JHK photometry of D-cloud IRAS sources (Massi+, 1999)
J/A+AS/104/233 : Emission-line stars in Vela Molecular Ridge (Pettersson+ 1994)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 I6 --- [SEC2010] Identification number
(<[SEC2010] IRAC NNNNNN> in Simbad)
8 I1 h RAh Hour of right ascension (J2000)
10- 11 I2 min RAm Minute of right ascension (J2000)
13- 16 F4.1 s RAs Second of right ascension (J2000)
18 A1 --- DE- Sign of declination (J2000)
19- 20 I2 deg DEd Degree of declination (J2000)
22- 23 I2 arcmin DEm Arcminute of declination (J2000)
25- 28 F4.1 arcsec DEs Arcsecond of declination (J2000)
30- 34 F5.2 mag Jmag ? 2MASS J-band magnitude (1)
36- 40 F5.2 mag Hmag ? 2MASS H-band magnitude (1)
42- 46 F5.2 mag Ksmag ? 2MASS Ks-band magnitude (1)
48- 52 F5.2 mag [3.6] Spitzer/IRAC 3.6um-band magnitude (1)
54- 58 F5.2 mag [4.5] Spitzer/IRAC 4.5um-band magnitude (1)
60- 64 F5.2 mag [5.8] ? Spitzer/IRAC 5.8um-band magnitude (1)
66- 70 F5.2 mag [8.0] ? Spitzer/IRAC 8.0um-band magnitude (1)
72- 75 F4.2 mag [24] ? Spitzer/MIPS 24um-band magnitude
counterpart (1)
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Note (1): Conversion into flux densities (Jansky) can be done by means of
the zero-mag fluxes that are: 280.9Jy (3.6um), 179.7Jy (4.5um),
115.0Jy (5.8um), 64.13Jy (8.0um), and 7.17Jy (24um). Typical errors
(in mag) are: 2MASS, J: 0.02-0.18, H: 0.02-0.17, K: 0.02-0.15; IRAC,
all bands: 0.1; MIPS 24um: 0.3.
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Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 I6 --- [SEC2010] Identification number
7 A1 --- f_[SEC2010] [c] c: Candidate young variable
9- 13 A5 --- Loc Source location (1)
15- 22 A8 --- Class YSO vs. other (AGB, XGAL (extragalactic), or
PHT (photosphere))
24 A1 --- Delmag [CDI] Δmag vs λ (D: decreasing,
C: constant or I: Increasing)
26 A1 --- Difmag [0±] Evolution of [3.6]-[4.5] vs. [4.5] (2)
28- 31 F4.1 --- E Ratio of the observed SED and the underlying
normalized K5-M5 photosphere (3)
33- 37 F5.3 Lsun Lirac IRAC luminosity
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Note (1): Location coded as follows:
O = outside the CO contours,
I = inside,
P = on a peak of warm gas.
IRS16 = the source lies within the IR cluster IRS16, although located
outside our CO map.
Note (2): Code as follows:
- = redder,
0 = constant,
+ = bluer color during a fading event
Note (3): Ratio of the observed SED and the underlying normalized K5-M5
photosphere, both integrated from J to 8um.
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History:
From electronic version of the journal
References:
Strafella et al. Catalog. 2010ApJ...719....9S 2010ApJ...719....9S
(End) Emmanuelle Perret [CDS] 09-Nov-2011