J/AJ/147/146 Spectroscopy of Tuc-Hor candidate members (Kraus+, 2014)
A stellar census of the Tucana-Horologium moving group.
Kraus A.L., Shkolnik E.L., Allers K.N., Liu M.C.
<Astron. J., 147, 146 (2014)>
=2014AJ....147..146K 2014AJ....147..146K
ADC_Keywords: Associations, stellar ; Stars, late-type ; Stars, nearby ;
Stars, M-type ; Stars, K-type ; Spectral types ; Spectroscopy ;
Equivalent widths ; Proper motions
Keywords: binaries: spectroscopic - stars: pre-main sequence -
open clusters and associations: individual: Tucana-Horologium -
stars: activity - stars: kinematics and dynamics - stars: low-mass
Abstract:
We report the selection and spectroscopic confirmation of 129 new
late-type (SpT=K3-M6) members of the Tucana-Horologium moving group, a
nearby (d∼40pc), young (τ∼40Myr) population of comoving stars. We
also report observations for 13 of the 17 known Tuc-Hor members in
this spectral type range, and that 62 additional candidates are likely
to be unassociated field stars; the confirmation frequency for new
candidates is therefore 129/191=67%. We have used radial velocities,
Hα emission, and Li6708 absorption to distinguish between
contaminants and bona fide members. Our expanded census of Tuc-Hor
increases the known population by a factor of ∼3 in total and by a
factor of ∼8 for members with SpT≥K3, but even so, the K-M dwarf
population of Tuc-Hor is still markedly incomplete. Our expanded
census allows for a much more detailed study of Tuc-Hor than was
previously feasible. The spatial distribution of members appears to
trace a two-dimensional sheet, with a broad distribution in X and Y,
but a very narrow distribution (±5pc) in Z. The corresponding
velocity distribution is very small, with a scatter of ±1.1km/s
about the mean UVW velocity for stars spanning the entire 50pc extent
of Tuc-Hor. We also show that the isochronal age (τ∼20-30Myr) and
the lithium depletion boundary age (τ∼40Myr) disagree, following
the trend in other pre-main-sequence populations for isochrones to
yield systematically younger ages. The Hα emission line strength
follows a trend of increasing equivalent width with later spectral
type, as is seen for young clusters. We find that moving group members
have been depleted of measurable lithium for spectral types of
K7.0-M4.5. None of our targets have significant infrared excesses in
the WISE W3 band, yielding an upper limit on warm debris disks of
F<0.7%. Finally, our purely kinematic and color-magnitude selection
procedure allows us to test the efficiency and completeness for
activity-based selection of young stars. We find that 60% of K-M
dwarfs in Tuc-Hor do not have ROSAT counterparts and would have been
omitted in X-ray-selected samples. In contrast, GALEX UV-selected
samples using a previously suggested criterion for youth achieve
completeness of 77% and purity of 78%, and we suggest new
SpT-dependent selection criteria that will yield >95% completeness for
τ∼40Myr populations with GALEX data available.
Description:
We obtained high-resolution spectra for our targets in three observing
runs in 2012 July, 2012 September, and 2013 February. We observed our
targets using the Magellan Inamori Kyocera Echelle (MIKE) optical
echelle spectrograph on the Clay telescope at Magellan Observatory.
For all observations we used the 0.7'' slit, which yields spectral
resolution of R=35000 across a range of λ=3350-9500Å. Since
our targets are relatively red, most only had useable signal on the
red chip (λ>5000Å).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 128 204 Selection criteria and observations of candidate
Tuc-Hor members
table2.dat 99 205 Spectroscopic results and membership assessments
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See also:
B/denis : The DENIS database (DENIS Consortium, 2005)
I/322 : UCAC4 Catalogue (Zacharias+, 2012)
V/139 : The SDSS Photometric Catalog, Release 9 (Adelman-McCarthy+, 2012)
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
I/284 : The USNO-B1.0 Catalog (Monet+ 2003)
J/ApJ/762/88 : Young stellar kinematic group candidate members (Malo+, 2013)
J/ApJ/753/147 : Herschel observations stars in THA (Donaldson+, 2012)
J/ApJ/758/56 : Young M dwarfs within 25pc. II. Kinematics (Shkolnik+, 2012)
J/ApJ/699/649 : Young M dwarfs within 25pc. I. (Shkolnik+, 2009)
J/AJ/134/2340 : Membership of Praesepe & Coma Berenices clusters (Kraus+, 2007)
J/AJ/132/866 : New M dwarfs in solar neighborhood (Riaz+, 2006)
J/A+A/460/695 : Search for Associations Containing Young stars (Torres+, 2006)
J/AJ/128/463 : A preliminary 20pc census from the NLTT catalogue (Reid+, 2004)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- St "Known" or "Candidate" member status
11- 26 A16 --- 2MASS 2MASS identifier of the known or candidate
Tuc-Hor member (HHMMSSss+DDMMSSs, J2000)
28- 40 A13 --- Name Common star name
42- 45 F4.1 mag Rmag [6.4/16.3] R-band magnitude from USNO-B1.0
survey (Monet et al. 2003, I/284) (1)
47- 51 F5.2 mag Kmag [4.19/11.28] Ks band magnitude (1)
53- 57 F5.1 mas/yr pmRA ? Proper motion in Right Ascension (µ) (2)
59- 64 F6.1 mas/yr pmDE ? Proper motion in Declination (µ) (2)
66- 69 F4.1 mas/yr e_pmDE ? Uncertainty in proper motion
71- 74 A4 --- SpT1 Spectral type from SED-fit SpTSED (3)
76- 78 F3.1 --- e_SpT1 Error in SpT1
80- 84 F5.2 mag mbol [6.44/14.09] Apparent bolometric magnitude (3)
86- 89 F4.2 mag e_mbol Error in mbol
91- 95 F5.2 mag DMph [-0.37/4.4] Photometric distance modulus (3)
97-100 F4.2 mag e_DMph Error in DMph
102-105 F4.1 mas/yr pmO-C ? Proper motion residual Δµ (5)
107-109 F3.1 mag DMkin ? Best-fit kinematic distance modulus
111-120 A10 "Y:M:D" Date UT date for our MIKE observations (6)
122-124 I3 s Exp [5/720] Exposure time (tint)
126-128 I3 --- S/N Signal/Noise ratio for each spectrum at 6600Å
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Note (1): Sources of the photometry are: USNO-B1.0 (I/284), 2MASS (II/246),
DENIS (B/denis), SDSS-DR9 (V/139), UCAC3(I/315); see Section 2.1 for
more details.
Note (2): Sources of the proper motions are: USNO-B1.0 (I/284),
Gould & Kollmeier 2004 (J/ApJS/152/103), PPMXL (I/317); see section 2.2
for more details.
Note (3): See Section 2.3 for details about the calculation of bolometric
fluxes, spectral type, and photometric distance modulus.
Note (5): The discrepancy between the observed proper motion and the best-fit
proper motion.
Note (6): Magellan Inamori Kyocera Echelle (MIKE) optical echelle spectrograph
on the Clay telescope at Magellan Observatory.
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Byte-by-byte Description of file:table2.dat
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Bytes Format Units Label Explanations
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1 A1 --- --- [J]
2- 17 A16 --- 2MASS 2MASS identifier of the known or candidate Tuc-Hor
member (HHMMSSss+DDMMSSs, J2000)
19- 31 A13 --- Name Common name
33- 38 F6.1 km/s RV Radial velocity (vrad) (7)
40- 43 F4.1 km/s e_RV Error in RV
45- 51 F7.2 km/s RVO-C Radial velocity discrepancy (Δvrad) (8)
53- 56 F4.1 km/s vsini Rotational velocity
58- 61 F4.1 km/s e_vsini Error in vsini
63- 66 A4 --- SpT MK spectral type (9)
68- 73 F6.2 0.1nm EWHa Hα equivalent width (in Å) (10)
75- 79 F5.1 0.1pm EWLi Liλ6708Å equivalent width in mÅ (10)
81 A1 --- MmRV [YN] Assessment of an object's membership in
Tuc-Hor based on radial velocity (11)
83 A1 --- MmHa [?YN] Assessment of an object's membership in
Tuc-Hor based on the presence (or absence) of
lithium (11)
85 A1 --- MmLi [?YN] Assessment of an object's membership in
Tuc-Hor based on Hα emission (11)
87 A1 --- Mm [YN] Final assessment of an object's membership
in Tuc-Hor (11)
88 A1 --- u_Mm [?] Uncertainty flag on Mm
89 A1 --- --- [-]
90- 97 A8 --- n_Mm Criterion used for making that judgement
(RV, Hα, or Li) (11)
99 A1 --- f_Mm [a12] "a" indicates a possible field interloper
(see caption of Figure 12), "2" or "3" for
spectroscopic binaries (in tables 3 and 4 resp.)
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Note (7): Indicates the one-dimensional projection of the population's space
velocity vUVW onto the line of sight d toward that member.
Note (8): Difference between the observed radial velocity and the expected
radial velocity.
Note (9): The spectroscopic spectral types are likely uncertain by ±1
subclass, based on the shape of the χν2 surfaces shown in Figure 3.
Note (10): Based on the scatter for field objects in Figures 6 and 7, the
uncertainties in equivalent widths are ±0.05Å for Li6708 and
±0.1Å for Hα.
Note (11): See Section 5.1 for more details.
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History:
From electronic version of the journal
(End) Sylvain Guehenneux [CDS] 20-Jan-2015