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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents

ID: 225818.0, MPI für Astronomie / Publikationen_mpia
A rotational and variability study of a large
sample of PMS stars in NGC 2264
Authors:Lamm, M. H.; Bailer-Jones, C. A. L.; Mundt, R.; Herbst, W.; Scholz, A.
Date of Publication (YYYY-MM-DD):2004
Title of Journal:Astronomy and Astrophysics
Start Page:557
End Page:581
Review Status:not specified
Audience:Not Specified
Abstract / Description:We present the results of an extensive search
for periodic and irregular variable pre-main
sequence (PMS) stars in the young (2-4 Myr) open
cluster <ASTROBJ>NGC 2264</ASTROBJ>, based on
photometric monitoring using the Wide Field
Imager (WFI) on the 2.2 m telescope on La Silla
(Chile). In total, about 10 600 stars with
IC magnitudes between 9.8 mag and 21
mag have been monitored in our 34 arcmin ‚‚times;
33 arcmin field. Time series data were obtained
in the IC band in 44 nights between
Dec. 2000 and March 2001; altogether we obtained
88 data points per star. Using two different time
series analysis techniques (Scargle periodogram
and CLEAN) we found 543 periodic variable stars
with periods between 0.2 days and 15 days. Also,
484 irregular variable stars were identified
using a ‚‚chi;2-test. In addition we
have carried out nearly simultaneous
observations in V, RC and a
narrow-band H‚‚alpha; filter. The photometric
data enable us to reject background and
foreground stars from our sample of variable
stars according to their location in the
IC vs. (RC-IC)
colour-magnitude and (RC-H‚‚alpha;)
vs. (RC-IC) colour-colour
diagrams. We identified 405 periodic variable
and 184 irregular variable PMS stars as cluster
members using these two different tests. In
addition 35 PMS stars for which no significant
variability were detected could be identified as
members using an H‚‚alpha; emission index
criterion. This yields a total of 624 PMS stars
in NGC 2264, of which only 182 were previously
known. Most of the newly found PMS stars are
fainter than IC ‚‚sime; 15 mag and of
late spectral type (‚‚ga;M 2). We find that the
periodic variables, as a group, have a smaller
degree of variability and smaller H‚‚alpha;
index than the irregular variables. This suggests
that the sample of periodic variables is biased
towards weak-line T Tauri stars (WTTSs) while
most of the irregular variables are probably
classical T Tauri stars (CTTSs). We have
quantified this bias and estimated that the
expected fraction of WTTSs among PMS stars in the
cluster is 77%. This is relatively close to the
fraction of WTTSs among the periodic variables
which is 85%. We also estimated the total
fraction of variables in the cluster using only
two well selected concentrations of PMS stars
called NGC 2264 N ‚‚amp; S in which we can easily
estimate the total number of PMS stars. We find
that at least 74% of the PMS stars in the
cluster with IC‚‚le; 18.0 mag were
found to be variable (either periodic or
irregular) by our study. This number shows that
our search for PMS stars in NGC 2264 through
extensive and accurate photometric monitoring is
very efficient in detecting most PMS stars down
to at least IC=18.0 mag.
Free Keywords:galaxy: open clusters and associations:
; individual: NGC 2264; stars: pre-main sequence;
; stars: rotation; stars: activity; stars:
; starspots; methods: data analysis
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie
External Affiliations:K‚‚ouml;nigstuhl 17, 69117 Heidelberg, Germany),
AB(Max-Planck-Institut f‚‚uuml;r Astronomie,
K‚‚ouml;nigstuhl 17, 69117 Heidelberg, Germany),
AC(Max-Planck-Institut f‚‚uuml;r Astronomie,
K‚‚ouml;nigstuhl 17, 69117 Heidelberg, Germany),
AD(Van Vleck Obs., Wesleyan Univ., Middletown, CT
06459, USA), AE(Th‚‚uuml;ringer Landessternwarte
Tautenburg, Sternwarte 5, 07778 Tautenburg,
Identifiers:URL:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bi... [ID No:1]
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