J/MNRAS/465/1807 Deep OB star population in Carina (Mohr-Smith+, 2017)
The deep OB star population in Carina from the VST Photometric H-alpha Survey
(VPHAS+).
Mohr-Smith M., Drew J.E., Napiwotzki R., Simon-Diaz S., Wright N.J.,
Barentsen G., Eisloeffel J., Farnhill H. J., Greimel R., Monguio M.,
Kalari V., Parker Q.A., Vink J.S.
<Mon. Not. R. Astron. Soc. 465, 1807 (2017)>
=2017MNRAS.465.1807M 2017MNRAS.465.1807M (SIMBAD/NED BibCode)
ADC_Keywords: Galactic plane ; Stars, early-type ; Photometry, SDSS ;
Photometry, H-alpha ; Reddening
Keywords: surveys - stars: early-type - dust, extinction - Galaxy: disc -
open clusters and associations: general
Abstract:
Massive OB stars are critical to the ecology of galaxies, and yet our
knowledge of OB stars in the Milky Way, fainter than V∼12, remains
patchy. Data from the VST Photometric H-alpha Survey (VPHAS+) permit
the construction of the first deep catalogues of blue excess-selected
OB stars, without neglecting the stellar field. A total of 14900
candidates with 2MASS cross-matches are blue-selected from a 42
square-degree region in the Galactic longitude range
282°<l<293° Spectral energy distribution fitting is performed
on these candidates' combined VPHAS+ u/g/r/i and 2MASS J/H/K
magnitudes. This delivers: effective temperature constraints,
statistically separating O from early-B stars; high-quality extinction
parameters, A0 and RV (random errors typically <0.1). The high
confidence O-B2 candidates number 5915 and a further 5170 fit to later
B spectral type. Spectroscopy of 276 of the former confirms 97% of
them. The fraction of emission line stars among all candidate B stars
is 7-8%. Greyer (RV>3.5) extinction laws are ubiquitous in the
region, over the distance range 2.5-3kpc to ∼10kpc. Near prominent
massive clusters, RV tends to rise, with particularly large and
chaotic excursions to RV∼5 seen in the Carina Nebula. The data
reveal a hitherto unnoticed association of 108 O-B2 stars around the
O5If+ star LSS 2063 (l=289.77°, b=-1.22°). Treating the OB
star scale-height as a constant within the thin disk, we find an
orderly mean relation between extinction (A0) and distance in the
Galactic longitude range, 287.6°<l< 293.5°, and infer the
subtle onset of thin-disk warping. A halo around NGC 3603, roughly a
degree in diameter, of ∼500 O-B2 stars with 4<A0(mag)<7 is noted.
Description:
The sky positions and photometric measurements from VPHAS+ (and 2MASS)
for 14900 candidate OB stars blue-selected from the Carina region of
the Galactic plane are set out in the first 24 columns. The optical
magnitudes are expressed in the Vega system. These are followed by the
parameters and their error estimates obtained from main-sequence fits
to the optical/NIR magnitudes, along with the chi-squared measure of
goodness of fit (columns 25 to 33). For the 3 degrees of freedom
involved, chi-squared values up to 7.82 may be regarded as 'good
fits': 5915 objects are good fits in this sense and have estimated
effective temperatures high enough to place them into the O-B2 range.
The fitting process delivers effective temperatures, (highly
uncertain) distance moduli, and the extinction parameters, A0 and
RV. Subsequent columns (34 to 37) identify which candidates are:
good O-B2 fits; likely to be emission line stars (based on r-Halpha
excess); candidate sub-luminous stars; candidate higher-luminosity
evolved objects. The 'Notes' in column 38 provide information on
cross-identifications to known objects, where these exist. Columns 39
to 49 present spectroscopically-derived parameters and associated
errors for the subset of 276 stars with spectra.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
carinaob.dat 393 14900 Positions, photometry and derived parameters
for the OB candidates
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See also:
II/341 : VPHAS+ DR2 survey (Drew+, 2016)
J/ApJS/194/5 : Carina OB stars in the CCCP catalog (Gagne+, 2011)
J/ApJS/194/7 : X-ray properties of O and B stars in Carina (Naze+, 2011)
J/MNRAS/440/2036 : VPHAS+ survey synthetic colours (Drew+, 2014)
Byte-by-byte Description of file:carinaob.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- --- [VPHASOB1]
11- 15 I05 --- VPHAS-OB1 VPHASOB1NNNNN where NNNNN is Galactic
longitude ordered sequence number
17- 26 F10.6 deg RAdeg Right ascension (J2000.0)
28- 37 F10.6 deg DEdeg Declination (J2000.0)
39- 48 F10.6 deg GLON Galactic longitude
50- 58 F9.6 deg GLAT Galactic declination
60- 65 F6.3 mag umag u band magnitude (Vega)
67- 71 F5.3 mag e_umag u band random error
73- 78 F6.3 mag gmag g band magnitude (Vega)
80- 84 F5.3 mag e_gmag g band random error
86- 91 F6.3 mag rmag r band magnitude (Vega), taken with u,g
measurements and used in SED fitting
93- 97 F5.3 mag e_rmag r band random error
99-104 F6.3 mag r2mag ?=- r band magnitude (Vega), taken with Ha,i
106-110 F5.3 mag e_r2mag ?=- r2 band random error
112-117 F6.3 mag imag i band magnitude (Vega)
119-123 F5.3 mag e_imag i band random error
125-130 F6.3 mag Hamag ?=- narrowband Ha magnitude (Vega)
132-136 F5.3 mag e_Hamag ?=- Ha band random error
138-143 F6.3 mag Jmag 2MASS J band magnitude (Vega)
145-149 F5.3 mag e_Jmag J band random error
151-156 F6.3 mag Hmag 2MASS H band magnitude (Vega)
158-162 F5.3 mag e_Hmag H band random error
164-169 F6.3 mag Kmag 2MASS K band magnitude (Vega)
171-175 F5.3 mag e_Kmag K band random error
177-181 F5.3 arcsec Xmatch Cross-match separation between VPHAS+
and 2MASS sky positions
183-187 F5.3 [K] logTeff log(effective temperature) from SED
fit (1)
189-193 F5.3 [K] E_logTeff Upper uncertainty on logTeff (2)
195-199 F5.3 [K] e_logTeff Lower uncertainty on logTeff (3)
201-206 F6.3 mag A0 Monochromatic extinction at 5495Å,
from SED fit (1)
208-212 F5.3 mag E_A0 Upper uncertainty on A0 (2)
214-218 F5.3 mag e_A0 Lower uncertainty on A0 (3)
220-224 F5.3 --- Rv Extinction law parameter from SED fit (1)
226-230 F5.3 --- E_Rv Upper uncertainty on Rv (2)
232-236 F5.3 --- e_Rv Lower uncertainty on Rv (3)
238-242 F5.2 mag mu Distance modulus from SED fit, if on
the main sequence (1)
244-247 F4.2 mag E_mu Upper uncertainty on mu (2)
249-252 F4.2 mag e_mu Lower uncertainty on mu (3)
254-260 F7.2 --- chi2 chi-squared of SED fit, obtained for
posterior median parameter values
262 I1 --- goodOB [0/1] if 1, chi2 < 7.82, otherwise 0
264 I1 --- EM [0/1] if 1, selected as likely emission line
objects, otherwise 0
266 I1 --- SUB [0/1] if 1, star is a candidate subluminous
object, otherwise 0
268 I1 --- LUM [0/1] if 1, star is a candidate
higher-luminosity evolved object,
otherwise 0
270-318 A49 --- Notes Comments, including SIMBAD cross
identification name where it exists
320 I1 --- SPEC [0/1]? if 1, spectroscopic parameters are
available, otherwise 0
322-329 A8 --- SpecMod Indicates source of model fit to
AAOmega spectrum (FASTWIND or TLUSTY)
331-336 F6.4 [K] logTeffsp ?=- log(effective temperature) from model
atmosphere fit to spectrum (1)
338-343 F6.4 [K] E_logTeffsp ?=- Upper uncertainty on speclogTeff (2)
345-352 F8.6 [K] e_logTeffsp ?=- Lower uncertainty on speclogTeff (3)
354-357 F4.2 [cm/s2] logg ?=- Surface gravity from model atmosphere
fit to spectrum (1)
359-366 F8.6 [cm/s2] E_logg ?=- Upper uncertainty on logg (2)
368-375 F8.6 [cm/s2] e_logg ?=- Lower uncertainty on logg (3)
377-381 F5.1 km/s vsini ?=- Projected rotational velocity from
model atmosphere fit to spectrum (1)(4)
383-387 F5.1 km/s E_vsini ?=- Upper uncertainty on vsini (2)(4)
389-393 F5.1 km/s e_vsini ?=- Lower uncertainty on vsini (3)(4)
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Note (1): value given is median of the posterior distribution
Note (2): error given is the offset from the median to the 84th percentile of
the posterior distribution
Note (3): error given is the offset from the median to the 16th percentile of
the posterior distribution
Note (4): the projected rotational velocity estimates from the spectroscopic
fits are give for completeness, but must be regarded as more uncertain than
formally stated, particularly where the vsini estimate is less than the
resolution of the spectra (∼230km/s).
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Acknowledgements:
M. Mohr-Smith and J. E. Drew, j.drew(at)herts.ac.uk
(End) Patricia Vannier [CDS] 08-Nov-2016