Star formation

About: Star formation is a research topic. Over the lifetime, 37405 publications have been published within this topic receiving 1808161 citations. The topic is also known as: astrogenesis.

Astrophysical Data: Planets and Stars

Abstract: This volume collects reference information for astronomers and astrophysicists, ranging from fundamental physical constants to orbital data for selected asteroids. For the Earth and planets, it includes, for example, data on mass, orbits and atmospheres. There are chapters on the Sun, on stars in general, on bright and nearby stars, and on Wolf-Rayet stars. On a large scale, there are data on star clusters and associations, on region of star formation and other nebulae of various kinds. Finally, the book includes chapters on dwarf stars, pulsars, interacting binaries, symbiotic stars, supernovae remnants and X-ray and gamma-ray sources. This dictionary/encyclopaedia on fundamental astrophysics, extragalactic objects, cosmology and cosmogony is intended for students and researchers in astronomy and astrophysics.

Towards an understanding of the rapid decline of the cosmic star formation rate

Abstract: We present a first analysis of deep 24 micron observations with the Spitzer Space Telescope of a sample of nearly 1500 galaxies in a thin redshift slice, 0.65 2x10^10 solar masses) are undergoing a period of intense star formation above their past-averaged SFR. In contrast, less than 1% of equally-massive galaxies in the local universe have similarly intense star formation activity. Morphologically-undisturbed galaxies dominate the total infrared luminosity density and SFR density: at z~0.7, more than half of the intensely star-forming galaxies have spiral morphologies, whereas less than \~30% are strongly interacting. Thus, a decline in major-merger rate is not the underlying cause of the rapid decline in cosmic SFR since z~0.7. Physical properties that do not strongly affect galaxy morphology - for example, gas consumption and weak interactions with small satellite galaxies - appear to be responsible.

Late-type members of young stellar kinematic groups - I. Single stars

Abstract: This is the first paper of a series aimed at studying the properties of late-type members of young stellar kinematic groups. We concentrate our study on classical young moving groups such as the Local Association (Pleiades moving group, 20-150 Myr), IC 2391 supercluster (35 Myr), Ursa Major group (Sirius supercluster, 300 Myr), and Hyades supercluster (600 Myr), as well as on recently identified groups such as the Castor moving group (200 Myr). In this paper we compile a preliminary list of single late-type possible members of some of these young stellar kinematic groups. Stars are selected from previously established members of stellar kinematic groups based on photometric and kinematic properties as well as from candidates based on other criteria such as their level of chromospheric activity, rotation rate and lithium abundance. Precise measurements of proper motions and parallaxes taken from the Hipparcos Catalogue, as well as from the Tycho-2 Catalogue, and published radial velocity measurements are used to calculate the Galactic space motions (U, V W) and to apply Eggen's kinematic criteria in order to determine the membership of the selected stars to the different groups. Additional criteria using age-dating methods for late-type stars will be applied in forthcoming papers of this series. A further study of the list of stars compiled here could lead to a better understanding of the chromospheric activity and their age evolution, as well as of the star formation history in the solar neighbourhood. In addition, these stars are also potential search targets for direct imaging detection of substellar companions.

The Disk Population of the Taurus Star-Forming Region

Abstract: We have analyzed nearly all images of the Taurus star-forming region at 3.6, 4.5, 5.8, 8.0, and 24??m that were obtained during the cryogenic mission of the Spitzer Space Telescope (46 deg2) and have measured photometry for all known members of the region that are within these data, corresponding to 348 sources, or 99% of the known stellar population. By combining these measurements with previous observations with the Spitzer Infrared Spectrograph and other facilities, we have classified the members of Taurus according to whether they show evidence of circumstellar disks and envelopes (classes I, II, and III). Through these classifications, we find that the disk fraction in Taurus, N(II)/N(II+III), is ~75% for solar-mass stars and declines to ~45% for low-mass stars and brown dwarfs (0.01-0.3 M ?). This dependence on stellar mass is similar to that measured for Chamaeleon I, although the disk fraction in Taurus is slightly higher overall, probably because of its younger age (1?Myr versus 2-3?Myr). In comparison, the disk fraction for solar-mass stars is much lower (~20%) in IC 348 and ? Ori, which are denser than Taurus and Chamaeleon I and are roughly coeval with the latter. These data indicate that disk lifetimes for solar-mass stars are longer in star-forming regions that have lower stellar densities. Through an analysis of multiple epochs of Spitzer photometry that are available for ~200 Taurus members, we find that stars with disks exhibit significantly greater mid-infrared (mid-IR) variability than diskless stars, which agrees with the results of similar variability measurements for a smaller sample of stars in Chamaeleon I. The variability fraction for stars with disks is higher in Taurus than in Chamaeleon I, indicating that the IR variability of disks decreases with age. Finally, we have used our data in Taurus to refine the observational criteria for primordial, evolved, and transitional disks. The ratio of the number of evolved and transitional disks to the number of primordial disks in Taurus is 15/98 for spectral types of K5-M5, indicating a timescale of 0.15 ? ?primordial ~ 0.45?Myr for the clearing of the inner regions of optically thick disks. After applying the same criteria to older clusters and associations (2-10?Myr) that have been observed with Spitzer, we find that the proportions of evolved and transitional disks in those populations are consistent with the measurements in Taurus when their star formation histories are properly taken into account.

The 2-10 keV luminosity as a Star Formation Rate indicator

Abstract: Radio and far infrared luminosities of star forming galaxies follow a tight linear relation. Making use of BeppoSAX and ASCA observations of a well-defined sample of star forming galaxies, we argue that a tight linear relation holds between the 2-10 keV X-ray luminosity and both the radio and far infrared ones. It is suggested that the hard X-ray emission is directly related to the Star Formation Rate. Preliminary results obtained from deep Chandra and radio observations of the Hubble Deep Field North show that a similar relation might hold also at high (0.2