J/ApJ/799/53 YSO/MS star models in the central molecular zone (Koepferl+, 2015)
Main-sequence stars masquerading as young stellar objects in the central
molecular zone.
Koepferl C.M., Robitaille T.P., Morales E.F.E., Johnston K.G.
<Astrophys. J., 799, 53 (2015)>
=2015ApJ...799...53K 2015ApJ...799...53K
ADC_Keywords: Models ; YSOs ; Photometry, infrared ; Stars, giant
Keywords: Galaxy: center; radiative transfer; stars: formation;
stars: pre-main sequence; stars: protostars
Abstract:
In contrast to most other galaxies, star formation rates in the Milky
Way can be estimated directly from young stellar objects (YSOs). In
the central molecular zone the star formation rate calculated from the
number of YSOs with 24µm emission is up to an order of magnitude
higher than the value estimated from methods based on diffuse emission
(such as free-free emission). Whether this effect is real or whether
it indicates problems with either or both star formation rate measures
is not currently known. In this paper, we investigate whether
estimates based on YSOs could be heavily contaminated by more evolved
objects such as main-sequence stars. We present radiative transfer
models of YSOs and of main-sequence stars in a constant ambient medium
which show that the main-sequence objects can indeed mimic YSOs at
24µm. However, we show that in some cases the main-sequence models
can be marginally resolved at 24µm, whereas the YSO models are
always unresolved. Based on the fraction of resolved MIPS 24µm
sources in the sample of YSOs previously used to compute the star
formation rate, we estimate the fraction of misclassified "YSOs" to be
at least 63%, which suggests that the star formation rate previously
determined from YSOs is likely to be at least a factor of three too
high.
Description:
Here we present input (spectral type, envelope infall rate, stage,
ambient medium, dust type) and output (magnitude in UKIDSS 2.2um, IRAC
8um, and MIPS 24um and the maximum surface brightness in PACS 70um,
MIPS 24um HWHM) parameters of the 660 models of YSOs and main-sequence
stars in an ambient density environment as well as the models of the
supergiants.
We used the three-dimensional Monte Carlo radiative transfer code
Hyperion (Robitaille 2011A&A...536A..79R 2011A&A...536A..79R) to compute the temperature
distribution and create synthetic images.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table3.dat 55 696 Parameters and measurements from our models
--------------------------------------------------------------------------------
See also:
II/316 : UKIDSS-DR6 Galactic Plane Survey (Lucas+ 2012)
II/295 : Spitzer IRAC survey of the galactic center (Ramirez+, 2008)
J/ApJ/736/133 : Spitzer-IRS study of YSOs in galactic center (An+, 2011)
J/ApJS/181/321 : Properties of Spitzer c2d dark clouds (Evans+, 2009)
J/ApJS/181/227 : Catalog of 24um sources toward Galactic Center (Hinz+, 2009)
J/ApJ/702/178 : YSOs in the central 400pc of the Galaxy (Yusef-Zadeh+, 2009)
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 A4 --- Class Stellar classification (1)
6- 9 E4.0 Msun/yr Infall [0/0.0003] Infall rate
11- 13 A3 --- Stage YSO stage ("0/1" or "2+")
15- 19 E5.1 g/cm3 Den Ambient density (1021, 3x1021, or 10-20)
21 A1 --- PAH [x-] PAH dust present: x=yes
23- 28 F6.2 mag Kmag [4/178] UKIDSS K band (2.2 micron) magnitude
30- 34 F5.2 mag [8.0] [-1.7/36.4] Spitzer/IRAC 8 micron band magnitude
36- 40 F5.2 mag [24] [-5.5/19.7] Spitzer/MIPS 24 micron band magnitude
42- 50 F9.2 MJy/sr SB70 [2.4/346049] Herschel/PACS 70 micron band
maximum surface brightness
52- 55 F4.2 arcsec HWHM [3/5.3] Half-Width at Half-Maximum of
24 micron image
--------------------------------------------------------------------------------
Note (1): Stellar data used in radiative transfer setup as follows:
-------------------------------------
SpT Temp Lum Rad Mass
(K) (Lsun) (Rsun) (Msun)
-------------------------------------
O5 44500 790000 15 60.
O6 41000 420000 13 37.
O8 35800 170000 11 23.
B0 30000 52000 8.4 17.5
B1 25400 16000 6.5 13. (a)
B2 22000 5700 5.2 10. (a)
B3 18700 1900 4.2 7.6
B5 15400 830 4.1 5.9
B8 11900 180 3.2 3.8
A0 9520 54 2.7 2.9
A5 8200 14 1.9 2.0
-------------------------------------
(a) = Values from interpolation of stellar data (See table 1)
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 11-Jun-2015