666 research outputs found
Bayesian analysis to identify new star candidates in nearby young stellar kinematic groups
We present a new method based on a Bayesian analysis to identify new members
of nearby young kinematic groups. The analysis minimally takes into account the
position, proper motion, magnitude and color of a star, but other observables
can be readily added (e.g. radial velocity, distance). We use this method to
find new young low-mass stars in the \beta Pictoris (\beta PMG) and AB Doradus
(ABDMG) moving groups and in the TW Hydrae (TWA), Tucana-Horologium (THA),
Columba, Carina and Argus associations. Starting from a sample of 758 mid-KM
(K5V-M5V) stars showing youth indicators such as H\alpha\ and X-ray emission,
our analysis yields 215 new highly probable low-mass members of the kinematic
groups analyzed. One is in TWA, 37 in \beta PMG, 17 in THA, 20 in Columba, 6 in
Carina, 50 in Argus, 33 in ABDMG, and the remaining 51 candidates are likely
young but have an ambiguous membership to more than one association. The false
alarm rate for new candidates is estimated to be 5% for \beta PMG and TWA, 10%
for THA, Columba, Carina and Argus, and 14% for ABDMG. Our analysis confirms
the membership of 58 stars proposed in the literature. Firm membership
confirmation of our new candidates will require measurement of their radial
velocity (predicted by our analysis), parallax and lithium 6708 {\AA}
equivalent width. We have initiated these follow-up observations for a number
of candidates and we have identified two stars (2MASSJ0111+1526,
2MASSJ0524-1601) as very strong candidate members of the \beta PMG and one
strong candidate member (2MASSJ0533-5117) of the THA; these three stars have
radial velocity measurements confirming their membership and lithium detections
consistent with young age. Finally, we proposed that six stars should be
considered as new bona fide members of \beta PMG and ABDMG, one of which being
first identified in this work, the others being known candidates from the
literature.Comment: Accepted for publication in Ap
SACY - a Search for Associations Containing Young stars
The scientific goal of the SACY (Search for Associations Containing
Young-stars) was to identify possible associations of stars younger than the
Pleiades Association among optical counterparts of the ROSAT X-ray bright
sources. High-resolution spectra for possible optical counterparts later than
G0 belonging to HIPPARCOS and/or TYCHO-2 catalogs were obtained in order to
assess both the youth and the spatial motion of each target. More than 1000
ROSAT sources were observed, covering a large area in the Southern Hemisphere.
The newly identified young stars present a patchy distribution in UVW and XYZ,
revealing the existence of huge nearby young associations. Here we present the
associations identified in this survey.Comment: 8 pages, 2 figures, to appear in the Proceedings of Open Issues in
Local Formation and Early Stellar Evolution, Ouro Preto, Brazi
Mapping the Shores of the Brown Dwarf Desert III: Young Moving Groups
We present the results of an aperture masking interferometry survey for
substellar companions around 67 members of the young (~8-200Myr) nearby
(~5-86pc) AB Doradus, Beta Pictoris, Hercules-Lyra, TW Hya, and
Tucana-Horologium stellar associations. Observations were made at near infrared
wavelengths between 1.2-3.8 microns using the adaptive optics facilities of the
Keck II, VLT UT4, and Palomar Hale Telescopes. Typical contrast ratios of
~100-200 were achieved at angular separations between ~40-320mas, with our
survey being 100% complete for companions with masses below 0.25\msolar across
this range. We report the discovery of a \msolar companion to
HIP14807, as well as the detections and orbits of previously known stellar
companions to HD16760, HD113449, and HD160934. We show that the companion to
HD16760 is in a face-on orbit, resulting in an upward revision of its mass from
\mjupiter to \msolar. No substellar
companions were detected around any of our sample members, despite our ability
to detect companions with masses below 80\mjupiter for 50 of our targets: of
these, our sensitivity extended down to 40\mjupiter around 30 targets, with a
subset of 22 subject to the still more stringent limit of 20\mjupiter. A
statistical analysis of our non-detection of substellar companions allows us to
place constraints on their frequency around ~0.2-1.5\msolar stars. In
particular, considering companion mass distributions that have been proposed in
the literature, we obtain an upper limit estimate of ~9-11% for the frequency
of 20-80\mjupiter companions between 3-30AU at 95% confidence, assuming that
their semimajor axes are distributed according to in this range.Comment: Accepted by Ap
How do you say ‘hello’? Personality impressions from brief novel voices
On hearing a novel voice, listeners readily form personality impressions of that speaker. Accurate or not, these impressions are known to affect subsequent interactions; yet the underlying psychological and acoustical bases remain poorly understood. Furthermore, hitherto studies have focussed on extended speech as opposed to analysing the instantaneous impressions we obtain from first experience. In this paper, through a mass online rating experiment, 320 participants rated 64 sub-second vocal utterances of the word ‘hello’ on one of 10 personality traits. We show that: (1) personality judgements of brief utterances from unfamiliar speakers are consistent across listeners; (2) a two-dimensional ‘social voice space’ with axes mapping Valence (Trust, Likeability) and Dominance, each driven by differing combinations of vocal acoustics, adequately summarises ratings in both male and female voices; and (3) a positive combination of Valence and Dominance results in increased perceived male vocal Attractiveness, whereas perceived female vocal Attractiveness is largely controlled by increasing Valence. Results are discussed in relation to the rapid evaluation of personality and, in turn, the intent of others, as being driven by survival mechanisms via approach or avoidance behaviours. These findings provide empirical bases for predicting personality impressions from acoustical analyses of short utterances and for generating desired personality impressions in artificial voices
RACE-OC Project: Rotation and variability in young stellar associations within 100 pc
Our goal is to determine the rotational and magnetic-related activity
properties of stars at different stages of evolution. We have focussed our
attention on 6 young loose stellar associations within 100 pc and ages in the
range 8-70 Myr: TW Hydrae (~8 Myr), beta Pictoris (~10 Myr), Tucana/Horologium,
Columba, Carina (~30 Myr), and AB Doradus (~70 Myr). Additional data on alpha
Persei and the Pleiades from the literature is also considered. Rotational
periods of stars showing rotational modulation due to photospheric magnetic
activity (i.e. starspots) have been determined applying the Lomb-Scargle
periodogram technique to photometric time-series obtained by the All Sky
Automated Survey (ASAS). The magnetic activity level has been derived from the
amplitude of the V lightcurves. We detected the rotational modulation and
measured the rotation periods of 93 stars for the first time, and confirmed the
periods of 41 stars already known from the literature. For further 10 stars we
revised the period determinations by other authors. The sample was augmented
with periods of 21 additional stars retrieved from the literature. In this way,
for the first time we were able to determine largest set of rotation periods at
ages of ~8, ~10 and ~30 Myr, as well as increase by 150\% the number of known
periodic members of AB Dor.The analysis of the rotation periods in young
stellar associations, supplemented by Orion Nebula Cluster (ONC) and NGC2264
data from the literature, has allowed us to find that in the 0.6 - 1.2 solar
masses range the most significant variations of the rotation period
distribution are the spin-up between 9 and 30 Myr and the spin-down between 70
and 110 Myr. Variations between 30 and 70 Myr are rather doubtful, despite the
median period indicates a significant spin-up.Comment: Accepted by Astronomy and Astrophysic
Search for Associations Containing Young stars (SACY): I. Sample & Searching Method
We report results from a high-resolution optical spectroscopic survey aimed
to search for nearby young associations and young stars among optical
counterparts of ROSAT All-Sky Survey X-ray sources in the Southern Hemisphere.
We selected 1953 late-type (B-V >= 0.6), potentially young, optical
counterparts out of a total of 9574 1RXS sources for follow-up observations. At
least one high-resolution spectrum was obtained for each of 1511 targets. This
paper is the first in a series presenting the results of the SACY survey. Here
we describe our sample and our observations. We describe a convergence method
in the (UVW) velocity space to find associations. As an example, we discuss the
validity of this method in the framework of the BetaPic Association.Comment: Accepted for publication in A&
SSPMJ1102-3431 brown dwarf characterization from accurate proper motion and trigonometric parallax
In 2005, Scholz and collaborators (Scholz et al. 2005) discovered, in a
proper motion survey, a young brown dwarf SSSPMJ1102-3431(SSSPMJ1102) of
spectral type M8.5, probable member of the TW Hydrae Association (TWA) and
possible companion of the T Tauri star TW Hya. The physical characterization of
SSSPMJ1102 was based on the hypothesis that it forms a binary system with TW
Hya. The recent discovery of a probable giant planet inside the TW Hya
protoplanetary disk with a very short-period (Setiawan et al. 2008) and a disk
around SSSPMJ1102 (Riaz and Gizis 2008) make it especially interesting and
important to measure well the physical parameters of SSSPMJ1102. Trigonometric
parallax and proper motion measurements of SSSPMJ1102 are necessary to test for
TWA membership and, thus, to determine the mass and age of this young brown
dwarf and the possibility that it forms a wide binary system with TW Hya. Two
years of regular observations at the ESO NTT/SUSI2 telescope, have enabled us
to determine the trigonometric parallax and proper motion of SSSPMJ1102. Our
parallax and proper motion determination allow us to precisely describe the
physical properties of this low mass object and to confirm its TWA membership.
Our results are not incompatible with the hypothesis that SSSPMJ1102 is a
binary companion of the star TW Hya.Comment: accepted for publication in A&
Photometric variability of the T Tauri star TW Hya on time scales of hours to years
MOST (Microvariability & Oscillations of STars) and ASAS (All Sky Automated
Survey) observations have been used to characterize photometric variability of
TW Hya on time scales from a fraction of a day to 7.5 weeks and from a few days
to 8 years, respectively. The two data sets have very different uncertainties
and temporal coverage properties and cannot be directly combined, nevertheless,
they suggests a global variability spectrum with "flicker noise" properties,
i.e. with amplitudes a ~ 1/sqrt(f), over >4 decades in frequency, in the range
f = 0.0003 to 10 cycles per day (c/d). A 3.7 d period is clearly present in the
continuous 11 day, 0.07 d time resolution, observations by MOST in 2007.
Brightness extrema coincide with zero-velocity crossings in periodic (3.56 d)
radial velocity variability detected in contemporaneous spectroscopic
observations of Setiawan et al. (2008) and interpreted as caused by a planet.
The 3.56/3.7 d periodicity was entirely absent in the second, four times longer
MOST run in 2008, casting doubt on the planetary explanation. Instead, a
spectrum of unstable single periods within the range of 2 - 9 days was
observed; the tendency of the periods to progressively shorten was well traced
using the wavelet analysis. The evolving periodicities and the overall
flicker-noise characteristics of the TW Hya variability suggest a combination
of several mechanisms, with the dominant ones probably related to the accretion
processes from the disk around the star.Comment: MNRAS submitte
Functioning styles of personality disorders and five-factor normal personality traits: a correlation study in Chinese students
BACKGROUND: Previous studies show that both the categorical and dimensional descriptors of personality disorders are correlated with normal personality traits. Recently, a 92-item inventory, the Parker Personality Measure (PERM) was designed as a more efficient and precise first-level assessment of personality disorders. Whether the PERM constructs are correlated with those of the five-factor models of personality needs to be clarified. METHODS: We therefore invited 913 students from poly-technical schools and colleges in China to answer the PERM, the Five-Factor Nonverbal Personality Questionnaire (FFNPQ), and the Zuckerman-Kuhlman Personality Questionnaire (ZKPQ). RESULTS: Most personality constructs had satisfactory internal alphas. PERM constructs were loaded with FFNPQ and ZKPQ traits clearly on four factors, which can be labelled as Dissocial, Emotional Dysregulation, Inhibition and Compulsivity, as reported previously. FFNPQ Openness to Experience, Conscientiousness and Extraversion formed another Factor, named Experience Hunting, which was not clearly covered by PERM or ZKPQ. CONCLUSION: The PERM constructs were loaded in a predictable way on the disordered super-traits, suggesting the PERM might offer assistance measuring personality function in clinical practice
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