J/A+A/579/A66 Accretion in ρ-Ophiucus (Manara+, 2015)
X-Shooter study of accretion in ρ-Ophiucus:
very low-mass stars and brown dwarfs.
Manara C.F., Testi L., Natta A., Alcala J.M.
<Astron. Astrophys., 579, A66-66 (2015)>
=2015A&A...579A..66M 2015A&A...579A..66M (SIMBAD/NED BibCode)
ADC_Keywords: Stars, pre-main sequence ; Accretion ; Stars, masses ;
Effective temperatures ; Equivalent widths
Keywords: stars: pre-main sequence - stars: formation - brown dwarfs -
protoplanetary disks - accretion, accretion disks -
clusters open and associations: individual: rho-Ophiucus
Abstract:
We present new VLT/X-Shooter optical and near-infrared spectra of a
sample of 17 candidate young low-mass stars and brown dwarfs located
in the ρ-Ophiucus cluster. We derived the spectral type and
extinction for all the targets, and then we determined their physical
parameters. All the objects but one have M*≲0.6M☉, and eight
have mass below or close to the hydrogen-burning limit. Using the
intensity of various permitted emission lines present in their
spectra, we determined the accretion luminosity and mass accretion
rates ({dot}(M)acc) for all the objects. When compared with previous
works targeting the same sample, we find that, in general, these
objects are not as strongly accreting as previously reported, and we
suggest that the reason is our more accurate estimate of the
photospheric parameters. We also compare our findings with recent
works in other slightly older star-forming regions, such as Lupus, to
investigate possible differences in the accretion properties, but we
find that the accretion properties for our targets have the same
dependence on the stellar and substellar parameters as in the other
regions. This leads us to conclude that we do not find evidence for a
different dependence of {dot}(M)acc with M* when comparing
low-mass stars and brown dwarfs. Moreover, we find a similar small
(≲1dex) scatter in the {dot}(M)acc-M* relation as in some of our
recent works in other star-forming regions, and no significant
differences in {dot}(M)acc due to different ages or properties of
the regions. The latter result suffers, however, from low statistics
and sample selection biases in the current studies. The small scatter
in the {dot}(M)acc-M* correlation confirms that mass accretion
rate measurements in the literature based on uncertain photospheric
parameters and single accretion indicators, such as the Hα
width, can lead to a scatter that is unphysically large. Our studies
show that only broadband spectroscopic surveys coupled with a detailed
analysis of the photospheric and accretion properties allows us to
properly study the evolution of disk accretion rates in star-forming
regions.
Description:
We report here about new data collected with the ESO/VLT X-Shooter
spectrograph during Pr.Id.085.C-0876 (PI Testi). This instrument
acquires spectra of the targets from λ∼300nm to λ∼2500nm
simultaneously, splitting the spectrum in three parts, usually
referred to as the UVB (λλ∼300-550nm), VIS
(λλ∼550-1050nm), and NIR (λλ∼1050-2500nm)
arms.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tabled1.dat 74 178 Properties of rho-Ophiuci young stellar objects
from Natta et al. (2006A&A...452..245N 2006A&A...452..245N,
Cat. J/A+A/452/245) using distance of 125pc
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See also:
J/A+A/452/245 : Near-IR photometry of PMS stars in rho Oph (Natta+, 2006)
Byte-by-byte Description of file: tabled1.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq Object sequential number
5- 11 A7 --- --- [ISO-Oph]
12- 14 I03 --- ISO ISO-Oph number
15 A1 --- m_ISO [ab] Multiplicity index on ISO
17- 19 A3 --- Class Class
21- 25 F5.2 [Lsun] logL* Stellar luminosity
27- 30 F4.2 [K] logTeff Effective temperature
32- 36 F5.2 [Msun] logM* ?=- Stellar mass (1)
38- 46 A9 --- Line Line identification
48 A1 --- l_EW(line) Limit flag on EW(line)
49- 52 F4.1 0.1nm EW(line) ?=- Line equivalent width
54 A1 --- l_logLline Limit flag on logLline
55- 59 F5.2 [Lsun] logLline ?=- Line luminosity
61 A1 --- l_logLacc Limit flag on logLacc
62- 66 F5.2 [Lsun] logLacc ?=- Accretion luminosity
68 A1 --- l_logdMacc/dt Limit flag on logdMacc/dt
69- 74 F6.2 [Msun/yr] logdMacc/dt ?=- Mass accretion rate
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Note (1): M* and age are derived using the evolutionary tracks of Baraffe et al.
(1998A&A...337..403B 1998A&A...337..403B, Cat. J/A+A/337/403) and assuming a single isochrone at
1Myr as explained in Rigliaco et al. (2011A&A...525A..47R 2011A&A...525A..47R, Cat. J/A+A/525/A47).
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 30-Sep-2015