J/ApJ/785/47 Sources around target stars in Upper Scorpius (Lafreniere+, 2014)
An adaptive optics multiplicity census of young stars in Upper Scorpius.
Lafreniere D., Jayawardhana R., van Kerkwijk M.H., Brandeker A., Janson M.
<Astrophys. J., 785, 47 (2014)>
=2014ApJ...785...47L 2014ApJ...785...47L (SIMBAD/NED BibCode)
ADC_Keywords: Associations, stellar ; Stars, double and multiple ;
Photometry, infrared
Keywords: binaries: general - brown dwarfs - stars: formation - stars: low-mass
Abstract:
We present the results of a multiplicity survey of 91 stars spanning
masses of ∼0.2-10 M☉ in the Upper Scorpius star-forming region,
based on adaptive optics imaging with the Gemini North telescope. Our
observations identified 29 binaries, 5 triples, and no higher order
multiples. The corresponding raw multiplicity frequency is
0.37±0.05. In the regime where our observations are
complete - companion separations of 0.1''-5'' (∼15-800 AU) with
magnitude limits ranging from K <9.3 at 0.1'' to K<15.8 at 5'' - the
multiplicity frequency is 0.270.04+0.05. For similar separations,
the multiplicity frequency in Upper Scorpius is comparable to that in
other dispersed star-forming regions, but is a factor of two to three
higher than in denser star-forming regions or in the field. Our sample
displays a constant multiplicity frequency as a function of stellar
mass. Among our sample of binaries, we find that both wider (>100 AU)
and higher-mass systems tend to have companions with lower
companion-to-primary mass ratios. Three of the companions identified
in our survey are unambiguously substellar and have estimated masses
below 0.04 M☉ (two of them are new discoveries from this
survey - 1RXS J160929.1-210524b and HIP 78530B - although we have
reported them separately in earlier papers). These three companions
have projected orbital separations of 300-900 AU. Based on a
statistical analysis factoring in sensitivity limits, we calculate an
occurrence rate of 5-40 MJup companions of ∼4.0% for orbital
separations of 250-1000 AU, compared to <1.8% at smaller separations,
suggesting that such companions are more frequent on wider orbits.
Description:
The target sample was selected from the list of 218 US members with
Spitzer observations that were studied by Carpenter et al.
(2006ApJ...651L..49C 2006ApJ...651L..49C; 2009, J/ApJ/705/1646) to investigate the
presence of circumstellar disks. The original Carpenter et al. sample
was built from a thorough literature compilation of US members, where
membership was assessed based on astrometry, H-R diagram position, Li
abundance, and X-ray emission, to which they applied further cuts to
ensure a high membership probability (e.g., on proper motions and
distances) and a good photometric quality. The observations were
obtained with the NIRI camera (Hodapp et al. 2003PASP..115.1388H 2003PASP..115.1388H) and
the ALTAIR AO system (Herriot et al. 2000SPIE.4007..115H 2000SPIE.4007..115H) at the
Gemini North Telescope (program GN-2008A-Q-45).
Objects:
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RA (ICRS) DE Designation(s)
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16 12 -23.4 Upper Scorpius = NAME Upper Sco
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 91 211 Sources detected around target stars
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See also:
J/MNRAS/373/95 : ZYJHK survey of Upper Sco association (Lodieu+, 2006)
J/ApJ/705/1646 : Debris disks in Upper Sco (Carpenter+, 2009)
J/MNRAS/418/1231 : New brown dwarfs in upper Sco (Dawson+, 2011)
J/ApJ/758/31 : IR photometry for members of Upper Sco (Luhman+, 2012)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1 A1 --- n_Name [F] Note on Name (1)
3- 33 A31 --- Name Source identifier (2)
35 A1 --- f_Name [eg] Flag on Name (3)
37- 42 F6.3 arcsec Sep Separation
44- 48 F5.3 arcsec e_Sep Uncertainty in Sep (4)
50- 55 F6.2 deg PA Position angle
57- 60 F4.2 deg e_PA Uncertainty in PA (4)
62- 66 F5.2 mag DelKmag ? K band magnitude difference
68- 71 F4.2 mag e_DelKmag ? Uncertainty in DelKmag
73- 84 F12.8 --- Edet ? Expected total number (5)
86- 88 I3 --- Ndet ? Actual number (6)
90- 91 A2 --- Status Status of candidate companion (7)
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Note (1): Note as follows:
F = Follow-up of an ambiguous candidate.
Note (2): When the same source appears on multiple lines, the corresponding
epochs are in the order given in Table 2.
Note (3): Flag as follows:
e = Measurements given are from our follow-up epoch, 2010-04-27;
g = Measurements given are from our first epoch, 2008-05-21.
Note (4): Only the measurement errors are given. There is an additional
systematic uncertainty in separation of 15 mas for <4'', 25 mas
for <8'' and 50 mas for <12'', as well as a systematic uncertainty
of 0.15 degrees in P.A. These uncertainties apply to comparison
with measurements made with other instruments, and to comparison
between the two epochs presented here.
Note (5): For the observations of our 91 targets stars, this is the expected
total number of detected background sources of the same brightness
or brighter and within the same angular separation. See text for
more detail.
Note (6): Actual number of such background sources detected by our survey.
Note (7): Status as follows:
C0 = bound companion based on statistical arguments (and sometimes known from
other work);
C1 = bound companion based on follow-up from this work;
C2 = bound companion based on other work;
B0 = background based on statistical arguments;
B1 = background based on follow-up from this work;
B2 = background based on other work;
? = undetermined.
See text sections 3.2 and 3.3 for more detail.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 01-Jun-2017