119019620
Pre-main sequence stars in open clusters - I. The DAY-I catalogue
Context. We present the basic ideas and first results from the project we are carrying out at present, the search for and characterisation of pre-main sequence (PMS) stars among the members of Galactic young clusters. The observations of 10 southern clusters, nine of them located in the Carina-Sagittarius spiral arm of the Milky Way are presented. Aims. We aim at listing candidate PMS member stars in young clusters. The catalogued stars will serve as a basis for future spectroscopic studies of individual objects to determine the properties of stellar formation in the last phases before the main sequence stage. Properties such as the presence of residual envelopes or disks, age spread among PMS members, and the possible presence of several episodes of star formation in the clusters, are to be addressed. Methods. Multicolour photometry in the $UBVR_{\rm C}I_{\rm C}$ system has been obtained for 10 southern young clusters in the fourth Galactic quadrant, located between Galactic longitudes l = 238° and l = 310°. For six clusters in the sample, the observations presented here provide the first published study based on CCD photometry. A quantitative comparison is performed with post-MS isochrones, and PMS isochrones from three different evolutionary models are used in the photometric membership analysis for possible PMS stars. Results. The observations produce photometric indices in the Johnson-Cousins photometric systems for a total of 26 962 stars. The matching of our pixel coordinates with corresponding fields in the 2MASS data base provides astrometric calibration for all cataloged stars and JHK 2MASS photometric indices for 60% of them. Post-MS cluster ages range from 4 to 60 Myr, whereas the photometric membership analysis assigns PMS membership to a total of 842 stars, covering an age range between 1 and 10 Myr. This information on the PMS candidate members has been collected into a catalogue, named DAY-I, which contains 16 entries for 842 stars in the field of 10 southern clusters.
15082396
Multiwavelength Analysis of the Young Open Cluster NGC 2362
We present a multiwavelength analysis of the young open cluster NGC 2362; UBVRCIC CCD photometric observations, together with available data in the Chandra database, near-infrared data from the Two Micron All Sky Survey (2MASS), and recently published Hα spectroscopy were used to get information about the evolutionary stage of the cluster and the main physical properties of its stellar content. Cluster membership is estimated for every individual star by means of zero-age main sequence (ZAMS) and isochrone fitting. The cluster is confirmed to host a rich population of pre-main-sequence (PMS) objects and to contain a large number of X-ray-emitting stars, which reach from the PMS members of GK spectral type up to the most luminous OB main-sequence (MS) members. The PMS cluster members show no significant age spread, and the comparison to both PMS and post-MS isochrones suggests an homogeneous age for all cluster members. The analysis allows us to assess the validity of currently used PMS evolutionary models and supports the suggestion of a well-defined positive correlation of the X-ray emission from PMS stars with their bolometric luminosity. Clear differences are found between the X-ray activity properties of MS and PMS cluster members, both in the relation between X-ray luminosity and bolometric luminosity, and in spectral properties as well.
16422495
A young double stellar cluster in a HII region, emerging from its parent molecular cloud ⋆
Aims. We investigate the star formation occurring in the region towards IRAS 07141-0920 contained in the HII region Sh2-294 (S294). We report the discovery ��� of a new young double stellar cluster, and we describe its properties. Methods. High-resolution optical UBVRI and Hα images obtained with ALFOSC mounted on the Nordic Optical Telescope (NOT), near-infrared JHKS images obtained with NOTCam at the Nordic Optical Telescope, and VLT/ISAAC images obtained through the H2 (2.12 µm) filter were all used to make photometric and morphological studies of the point sources and the nebula seen towards Sh2-294. Identification of PMS members was done using three different methods: comparison with isochrones in optical colour−magnitude diagrams and detection of either near-IR excess or Hα emission. Results. The optical images reveal an emission nebula rich in morphological details. The nebula is composed mainly of ultraviolet scattered light and of Hα emission with local morphological features conveying an impression of strong dynamical complexity. Contrasting with the bright parts of the nebula, opaque patches are seen. They appear elongated, filamentary, or clumpy. Our optical photometry confirms that the identification of the illuminator of the nebula is likely to be a B0.5V star located at a distance of about 3.2 kpc. Our high-resolution near-IR images reveal an embedded cluster, extending about 2 pc and exhibiting sub-clustering: a denser, more condensed, subcluster surrounding the optical high-mass B0.5V illuminator star; and a more embedded, optically invisible, subcluster located towards the eastern, dark part of the nebula and including the luminous MSX source G224.1880+01.2407, a massive protostellar candidate that could be the origin of jets and extended features seen at 2.12 µm. The double cluster appears to be clearing the remaining molecular material of the parent cloud, creating patches of lower extinction and allowing some of the least reddened members to be detected in the optical images. We find 12 main-sequence (MS) and 143 pre-main sequence(PMS) members. The most massive star fits a 4 Myr, post-MS isochrone. The age of the optically selected PMS population is estimated to be 7− 8M yr. The IR-excess population shows sub-clustering on scales as small as 0.23 pc and is probably much younger.
37717744
RS1, custodial isospin and precision tests
We study precision electroweak constraints within a RS1 model with gauge fields and fermions in the bulk. The electroweak gauge symmetry is enhanced to SU(2)L × SU(2)R × U(1)B−L, thereby providing a custodial isospin symmetry sufficient to suppress excessive contributions to the T parameter. We then construct complete models, complying with all electroweak constraints, for solving the hierarchy problem, without supersymmetry or large hierarchies in the fundamental couplings. Using the AdS/CFT correspondence our models can be interpreted as dual to a strongly coupled conformal Higgs sector with global custodial isospin symmetry, gauge and fermionic matter being fundamental fields external to the CFT. This scenario has interesting collider signals, distinct from other RS models in the literature.
119855006
Reply to “Comment on ‘Hunting long-lived gluinos at the Pierre Auger Observatory”’
11501016
A Fat Higgs with a Fat top
A new variant of the supersymmetric fat Higgs model is presented in which the MSSM Higgses as well as the top quark are composite. The underlying theory is an s-confining SU(3) gauge theory with the MSSM gauge groups realized as gauged sub-groups of the chiral flavor symmetries. This motivates the large Yukawas necessary for the large top mass and SM-like Higgs of mass >> MZ in a natural way as the residual of the strong dynamics responsible for the composites. This removes fine-tuning associated with these couplings present in the original fat Higgs and ``new fat Higgs'' models, respectively.
16961898
Running into new territory in SUSY parameter space
The LEP-II bound on the light Higgs mass rules out the vast majority of parameter space left to the Minimal Supersymmetric Standard Model (MSSM) with weak-scale soft-masses. This suggests the importance of exploring extensions of the MSSM with non-minimal Higgs physics. In this article, we explore a theory with an additional singlet superfield and an extended gauge sector. The theory has a number of novel features compared to both the MSSM and Next-to-MSSM, including easily realizing a light CP-even Higgs mass consistent with LEP-II limits, tan β1, and a lightest Higgs which is charged. These features are achieved while remaining consistent with perturbative unification and without large stop-masses. Discovery modes at the Tevatron and LHC are discussed.