A Case Study of Low-Mass Star Formation Swift, Jonathan J; Welch, William J
The Astrophysical journal. Supplement series,
01/2008, Letnik:
174, Številka:
1
Journal Article
Recenzirano
Odprti dostop
This article synthesizes observational data from an extensive program aimed toward a comprehensive understanding of star formation in a low-mass star-forming molecular cloud. New observations and ...published data spanning from the centimeter wave band to the near-infrared reveal the high- and low-density molecular gas, dust, and pre-main-sequence stars in L1551. The total cloud mass of similar to 160 M unk contained within 0.9 pc has a dynamical timescale, l sub(dyn) = 1.1 Myr. Thirty-five pre-main-sequence stars with masses from similar to 0.1 to 1.5 M unk are selected to be members of the L1551 association constituting a total of 22 plus or minus 5 M unk of stellar mass. The observed star formation efficiency, SPE = 12%, while the total efficiency, 3FE unk, is estimated to fall between 9% and 15%. L1551 appears to have been forming stars for several l sub(dyn), with the rate of star formation increasing with time. Star formation has likely progressed from east to west, and there is clear evidence that another star or stellar system will form in the high column density region to the northwest of L1551 IRS 5. High-resolution, wide-field maps of L1551 in CO isotopologue emission display the structure of the molecular cloud at 1600 AU physical resolution. The super(13)CO emission clearly reveals the disruption of the ambient cloud by outflows in the line core and traces the interface between regions of outflow and quiescent gas in the line wings. Kinetic energy from outflows is being deposited back into the cloud on a physical scale unk approximately 0.05 pc at a rate, E sub(input) approximately 0.05 L unk The remaining energy afforded by the full mechanical luminosity of outflow in L1551 destroys the cloud or is otherwise lost to the greater interstellar medium. The C super(18)O emission is optically thin and traces well the turbulent velocity structure of the cloud. The total turbulent energy is close to what is expected from virial equilibrium. The turbulent velocities exist primarily on small scales in the cloud, and the energy spectrum of turbulent fluctuations, E(k) proportional to k super(-3), is derived by various methods to have beta approximately 1-2. The turbulent dissipation rate estimated using the results of current numerical simulations is E sub(dies) approximately E sub(input). This study reveals that stellar feedback is a significant factor in the evolution of the L1551 cloud.
Discerning the Form of the Dense Core Mass Function Swift, Jonathan J.; Beaumont, Christopher N.
Publications of the Astronomical Society of the Pacific,
02/2010, Letnik:
122, Številka:
888
Journal Article
Recenzirano
We investigate the ability to discern between lognormal and power-law forms for the observed mass function of dense cores in star-forming regions. After testing our fitting, goodness-of-fit, and ...model selection procedures on simulated data, we apply our analysis to 14 data sets from the literature. Whether the core mass function has a power-law tail or whether it follows a pure lognormal form cannot be distinguished from current data. From our simulations it is estimated that data sets from uniform surveys containing more than≈500
≈
500
cores with a completeness limit below the peak of the mass distribution are needed to definitively discern between these two functional forms. We also conclude that the width of the core mass function may be more reliably estimated than the power-law index of the high mass tail and that the width may also be a more useful parameter in comparing with the stellar initial mass function to deduce the statistical evolution of dense cores into stars.
This conceptual paper outlines why, when working in the international as opposed to the domestic environment, the success of a relationship marketing strategy is heavily dependent on levels of ...psychic distance. The higher the level of psychic distance, the greater the time and effort required to develop successful business relationships. At the different stages of relationship development, different variables of psychic distance assume relatively greater levels of importance which are likely to have implications for the implementation of a relationship marketing strategy.
The Battle of the Books and A Tale of a Tub are the most important works in the early satirical writings of Jonathan Swift. They were written between 1695 and 1704. They appear in Polish translation ...for the first time. In the dispute between the Ancients and the Moderns Swift was a staunch supporter of the Ancients. Their followers believed that classical and biblical thought is continuously influencing us. Swift ridiculed his contemporaries for their cult of science, their religious hypocrisy, for following literary trends, and he did it by brilliantly applying irony and grotesques, creatively construing multi-layered absurdities.
Abstract
We present high-cadence ultraviolet through near-infrared observations of the Type Ia supernova (SN Ia) 2023bee at
D
= 32 ± 3 Mpc, finding excess flux in the first days after explosion, ...particularly in our 10 minutes cadence TESS light curve and Swift UV data. Compared to a few other normal SNe Ia with early excess flux, the excess flux in SN 2023bee is redder in the UV and less luminous. We present optical spectra of SN 2023bee, including two spectra during the period where the flux excess is dominant. At this time, the spectra are similar to those of other SNe Ia but with weaker Si
ii
, C
ii,
and Ca
ii
absorption lines, perhaps because the excess flux creates a stronger continuum. We compare the data to several theoretical models on the origin of early excess flux in SNe Ia. Interaction with either the companion star or close-in circumstellar material is expected to produce a faster evolution than observed. Radioactive material in the outer layers of the ejecta, either from double detonation explosion or from a
56
Ni clump near the surface, cannot fully reproduce the evolution either, likely due to the sensitivity of early UV observable to the treatment of the outer part of ejecta in simulation. We conclude that no current model can adequately explain the full set of observations. We find that a relatively large fraction of nearby, bright SNe Ia with high-cadence observations have some amount of excess flux within a few days of explosion. Considering potential asymmetric emission, the physical cause of this excess flux may be ubiquitous in normal SNe Ia.
We report that Kepler Object of Interest 256 (KOI-256) is a mutually eclipsing post-common envelope binary (ePCEB), consisting of a cool white dwarf (Mlow * = 0.592 + or - 0.089 M sub(middot in ...circle), Rlow * = 0.01345 + or - 0.00091 R sub(middot in circle), T sub(eff) = 7100 + or - 700 K) and an active M3 dwarf (Mlow * = 0.51 + or - 0.16 M sub(middot in circle), Rlow * = 0.540 + or - 0.014 R sub(middot in circle), T sub(eff) = 3450 + or - 50 K) with an orbital period of 1.37865 + or - 0.00001 days. KOI-256 is listed as hosting a transiting planet-candidate by Borucki et al. and Batalha et ah; here we report that the planet-candidate transit signal is in fact the occultation of a white dwarf as it passes behind the M dwarf. We combine publicly-available long- and short-cadence Kepler light curves with ground-based measurements to robustly determine the system parameters. The occultation events are readily apparent in the Kepler light curve, as is spin-orbit synchronization of the M dwarf, and we detect the transit of the white dwarf in front of the M dwarf halfway between the occultation events. The size of the white dwarf with respect to the Einstein ring during transit (R sub(Ein) = 0.00473 + or - 0.00055 R sub(middot in circle)) causes the transit depth to be shallower than expected from pure geometry due to gravitational lensing. KOI-256 is an old, long-period ePCEB and serves as a benchmark object for studying the evolution of binary star systems as well as white dwarfs themselves, thanks largely to the availability of near-continuous, ultra-precise Kepler photometry.
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