J/ApJ/726/18 Young intermediate-mass stars in W5 (Koenig+, 2011)
Disk evolution in W5: intermediate-mass stars at 2-5 Myr.
Koenig X.P., Allen L.E.
<Astrophys. J., 726, 18 (2011)>
=2011ApJ...726...18K 2011ApJ...726...18K
ADC_Keywords: Photometry, infrared ; Photometry, SDSS ; Spectral types ;
Stars, A-type ; Stars, B-type ; YSOs ; Stars, emission
Keywords: accretion, accretion disks - circumstellar matter - infrared: stars -
protoplanetary disks - stars: pre-main sequence -
techniques: spectroscopic
Abstract:
We present the results of a survey of young intermediate-mass stars
(age<5Myr, 1.5M☉<M*≤15M☉) in the W5 massive star-forming
region. We use combined optical, near-infrared, and Spitzer Space
Telescope photometry and optical spectroscopy to define a sample of
stars of spectral types A and B and examine their infrared excess
properties. We find objects with infrared excesses characteristic of
optically thick disks, i.e., Herbig AeBe stars. These stars are rare:
<1.5% of the entire spectroscopic sample of A and B stars, and absent
among stars more massive than 2.4M☉. 7.5% of the A and B stars
possess infrared excesses in a variety of morphologies that suggest
their disks are in some transitional phase between an initial,
optically thick accretion state and later evolutionary states. We
identify four morphological classes based on the wavelength dependence
of the observed excess emission above theoretical photospheric levels:
(1) the optically thick disks; (2) disks with an optically thin excess
over the wavelength range 2-24um, similar to that shown by Classical
Be stars; (3) disks that are optically thin in their inner regions
based on their infrared excess at 2-8um and optically thick in their
outer regions based on the magnitude of the observed excess emission
at 24um; (4) disks that exhibit empty inner regions (no excess
emission at λ<8um) and some measurable excess emission at 24um.
A sub-class of disks exhibit no significant excess emission at
λ≤5.8um, have excess emission only in the Spitzer 8um band and
no detection at 24um. We discuss these spectral energy distribution
types, and suggest physical models for disks exhibiting these emission
patterns and additional observations to test these theories.
Description:
Our Spitzer IRAC and MIPS observations (PID 20300) of W5 are described
in detail in Koenig et al. (2008, Cat. J/ApJ/688/1142). The MIPS
observations were carried out on 2006 February 23 UT.
We used KeplerCam on the 1.2m telescope at FLWO to image six fields in
W5 in Sloan r and z filters on 2006 January 21. KeplerCam has a
monolithic 40962 CCD detector giving a 23.1'x23.1' fov. We observed
a further 6 fields in W5 on 2006 September 25 with MegaCam on the MMT.
We obtained optical spectra, from 2006 October to 2008 December, of
candidate intermediate-mass stars with the Hectospec multifiber
spectrograph mounted on the 6.5m MMT telescope on Mount Hopkins
(spectra range: 3700-9000Å with a resolution of 6.2Å.
Additional spectra were obtained, from 2007 September until 2008
December, using the FAST slit spectrograph mounted on the 1.5m
telescope at FLWO (range: 3800-7200Å, with a resolution of ∼6Å).
File Summary:
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FileName recl Records Explanations
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ReadMe 80 . This file
table1.dat 142 389 W5 IR excess spectral catalog
table2.dat 145 46 AB-type stars with IR excess
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See also:
II/306 : The SDSS Photometric Catalog, Release 8 (Adelman-McCarthy+, 2011)
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
J/MNRAS/415/1202 : BVI photometry in W5E HII region (Chauhan+, 2011)
J/ApJ/688/1142 : Star formation in W5: Spitzer observations (Koenig+, 2008)
J/ApJS/101/117 : UBVRIJHKLMNQ photometry in Taurus-Auriga (Kenyon+ 1995)
Byte-by-byte Description of file: table[12].dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- ID [1141/20326] ID number from Koenig et al. 2008,
Cat. J/ApJ/688/1142, <[KAG2008] NNNNN> in Simbad
7- 15 F9.6 deg RAdeg Right Ascension in decimal degrees (J2000)
17- 25 F9.6 deg DEdeg Declination in decimal degrees (J2000)
27- 31 F5.2 mag Jmag [2/17]? 2MASS J band magnitude
33- 34 I2 cmag e_Jmag ? Uncertainty in Jmag
36- 40 F5.2 mag Hmag [2/17]? 2MASS H band magnitude
42- 43 I2 cmag e_Hmag ? Uncertainty in Hmag
45- 49 F5.2 mag Ksmag [2/19]? 2MASS Ks band magnitude
51- 52 I2 cmag e_Ksmag ? Uncertainty in Ksmag
54- 58 F5.2 mag [3.6] [5/15] Spitzer/IRAC 3.6 micron band magnitude
60- 61 I2 cmag e_[3.6] Uncertainty in [3.6]
63- 67 F5.2 mag [4.5] [4/15] Spitzer/IRAC 4.5 micron band magnitude
69- 70 I2 cmag e_[4.5] Uncertainty in [4.5]
72- 76 F5.2 mag [5.8] [4/15]? Spitzer/IRAC 5.8 micron band magnitude
78- 79 I2 cmag e_[5.8] ? Uncertainty in [5.8]
81- 85 F5.2 mag [8.0] [3/14]? Spitzer/IRAC 8.0 micron band magnitude
87- 89 I3 cmag e_[8.0] ? Uncertainty in [8.0]
91- 95 F5.2 mag [24] [0.9/11]? Spitzer/MIPS 24 micron band magnitude
97- 99 I3 cmag e_[24] ? Uncertainty in [24]
101-105 F5.2 mag r'mag [9/22]? SDSS r' band magnitude
107-108 I2 cmag e_r'mag ? Uncertainty in r'mag
110-114 F5.2 mag z'mag [8/20]? SDSS z' band magnitude
116-117 I2 cmag e_z'mag ? Uncertainty in z'mag
119-122 A4 --- SpT MK spectral type and subtype (only A or B for
table 2)
124-126 F3.1 --- e_SpT [0.5/2] Uncertainty in spectral type
128-134 F7.2 0.1nm EWHa ? Hα equivalent width; in Angstroms
136-139 F4.2 mag AV [0.01/6.83]? V band extinction
141-142 I2 cmag e_AV ? Uncertainty in AV
144-145 A2 --- Disk [a-e] Disk morphology from IR excess for A and
B stars (2)
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Note (2): IR excess group as follows:
a = A and B star disks in type "a" resemble the low mass Class I (an
optically thick disk and an envelope) and II (an optically thick disk).
b = similar to the "anemic" disks seen in IC 348 by Lada et al. (2006,
Cat. J/AJ/131/1574)
d = The type "d" disks resemble the "transitional" disks (no infrared excess
shortward of 24um) in low-mass stars
c = The thin/thick disks in type "c" are not exactly like any of these
definitions of disks, but a similar type was noted by Malfait et al.
(1998A&A...331..211M 1998A&A...331..211M) in their survey of nearby Herbig AeBe stars.
de = Disks in the sub-class with excess only at 8um and no 24um detection
See section 3.3 and figure 10 for further explanations.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 14-Aug-2012