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K.6530+
No full textK.6530 + K.8335
Photograph by the Shumma alu team (FNS projects nos. 175970 and 205122
DEA 4530-6530 Course Syllabus - Fall 10
No full textDEA 4530-6530, Planning and Managing the Workplace, Course Syllabus by Instructor Frank Becker, Fall 201
DEA 4530/6530 Course Syllabus - Fall 09
No full textDEA 4530/6530, Planing and Managing the Workplace, Course Syllabus by Instructor Franklin Becker, Fall 200
Mass segregation in very young open clusters: A case study of NGC 2244 and NGC 6530
No full textWe derive the proper motions, membership probabilities, and velocity dispersions of stars in the regions of the young (similar to 2 - 4 Myr old) open clusters NGC 2244 ( the central cluster in the Monoceros R2 association) and NGC 6530 ( the dominant cluster in the Sgr OB1 association) from photographic plate material obtained at Shanghai Astronomical Observatory, with time baselines of 34 and 87 yr, respectively. Both clusters show clear evidence of mass segregation, but they do not exhibit any significant velocity- mass ( or, equivalently, velocity- luminosity) dependence. This provides strong support for the suggestion that the observed mass segregation is at least partially due to the way in which star formation has proceeded in these complex star- forming regions ("primordial'' mass segregation). Based on arguments related to the clusters' published initial mass functions, in conjunction with our new measurements of their internal velocity dispersions (similar to 35 and 8 km s(-1) for NGC 2244 and NGC 6530, respectively), we provide strong arguments in favor of the dissolution of NGC 2244 on very short timescales, while we speculate that NGC 6530 may be more stable against the effects of internal two- body relaxation. However, this latter object may well be destroyed by the strong tidal field prevalent at its location in the Galactic plane in the direction of the Galactic center
Kinematic signatures of cluster formation from cool collapse in the Lagoon Nebula cluster NGC 6530
Get PDFWe examine the mass dependence of the velocity dispersion of stars in the young cluster NGC 6530 to better understand how it formed. Using a large sample of members we find that the proper motion velocity dispersion increases with stellar mass. While this trend is the opposite of that predicted if the cluster were developing energy equipartition, it is in agreement with recent N-body simulations that find such a trend develops because of the Spitzer instability. In these simulations the massive stars sink to the centre of the cluster and form a self-gravitating system with a higher velocity dispersion. If the cluster has formed by the cool collapse of an initially substructured distribution, then this occurs within 1–2 Myr, in agreement with our observations of NGC 6530. We therefore conclude that NGC 6530 formed from much more extended initial conditions and has since collapsed to form the cluster we see now. This cluster formation model is inconsistent with the idea that all stars form in dense, compact clusters and provides the first dynamical evidence that star clusters can form by hierarchical mergers between subclusters
Pulsating pre-main sequence stars in IC 4996 and NGC 6530
No full textContext. Asteroseismology of pulsating pre-main sequence (PMS) stars has the potential of testing the validity of current models of PMS structure and evolution. As a first step, a sufficiently large sample of pulsating PMS stars has to be established, which allows to select candidates optimally suited for a detailed asteroseismological analysis based on photometry from space or ground based network data. Aims. A search for pulsating PMS members in the young open clusters IC 4996 and NGC 6530 has been performed to improve the sample of known PMS pulsators. As both clusters are younger than 10 million years, all members with spectral types later than A0 have not reached the zero-age main sequence yet. Hence, IC 4996 and NGC 6530 are most suitable to search for PMS pulsation among their A- and F-type cluster stars. Methods. CCD time series photometry in Johnson B and V filters has been obtained for 1C 4996 and NGC 6530. The resulting light curves for 113 stars in IC 4996 and 194 stars in NGC 6530 have been subject to detailed frequency analyses. Results. 2 6 Scuti-like PMS stars have been discovered in IC 4996 and 6 in NGC 6530. For another PMS star in each cluster, pulsation can only be suspected. According to the computed pulsation constants, the newly detected PMS stars seem to prefer to pulsate in a similar fashion to the classical 6 Scuti stars, and with higher overtone modes. ESO 2006
A multiwavelength study of star formation in the very young open cluster NGC 6530
Get PDFThe distance and formation history of the very young open cluster NGC 6530
were investigated by studying a total of 132 probable member stars of this
open cluster. It was concluded that the distance to NGC 6530 is
, and its interstellar reddening is 030.
Furthermore, we conclude that the extinction law of the intracluster material
is normal (i.e. RV = 3.1), but anomalous extinction laws were found for
several more embedded stars in the cluster. Of the 132 stars included in this
study, 11 are suspected to be variable, five show Hα in emission and
nine show an infrared excess. Among the member stars of NGC 6530, three were
found to be part of the Herbig Ae/Be stellar class, whereas two others are
possible members of this stellar group as well. Also, one cluster member
is probably a new massive post-AGB star, whereas the same could possibly
apply to another member star. Finally, from the distribution of
post- and pre-main sequence stars in the cluster's HR-diagram, it was
concluded that the process of star formation in NGC 6530 must have started a
few times 107 years ago and, for the less massive stars, is probably
still going on today
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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