Lyman alpha initiated winds in late-type stars

The IUE survey of late-type stars revealed a sharp division in the HR diagram between stars with solar type spectra (chromosphere and transition region lines) and those with non-solar type spectra (only chromosphere lines). Models of both hot coronae and cool wind flows were calculated using stellar model chromospheres as starting points for stellar wind calculations in order to investigate the possibility of having a supersonic transition locus in the HR diagram dividing hot coronae from cool winds. From these models, it is concluded that the Lyman alpha flux may play an important role in determining the location of a stellar wind critical point. The interaction of Lyman alpha radiation pressure with Alfven waves in producing strong, low temperature stellar winds in the star Arcturus is examined

Very high resolution UV and X-ray spectroscopy and imagery of solar active regions

A scientific investigation of the physics of the solar atmosphere, which uses the techniques of high resolution soft X-ray spectroscopy and high resolution UV imagery, is described. The experiments were conducted during a series of three sounding rocket flights. All three flights yielded excellent images in the UV range, showing unprecedented spatial resolution. The second flight recorded the X-ray spectrum of a solar flare, and the third that of an active region. A normal incidence multi-layer mirror was used during the third flight to make the first astronomical X-ray observations using this new technique

A Significant Population of Candidate New Members of the ρ Ophiuchi Cluster

We present a general method for identifying the pre-main-sequence population of any star-forming region, unbiased with respect to the presence or absence of disks, in contrast to samples selected primarily via their mid-infrared emission from Spitzer surveys. We have applied this technique to a new, deep, wide-field, near-infrared imaging survey of the ρ Ophiuchi cloud core to search for candidate low-mass members. In conjunction with published Spitzer IRAC photometry and least-squares fits of model spectra (COND, DUSTY, NextGen, and blackbody) to the observed spectral energy distributions, we have identified 948 candidate cloud members within our 90% completeness limits of J = 20.0, H = 20.0, and Ks = 18.50. This population represents a factor of ~3 increase in the number of known young stellar objects in the ρ Ophiuchi cloud. A large fraction of the candidate cluster members (81% ± 3%) exhibit infrared excess emission consistent with the presence of disks, thus strengthening the possibility of their being bona fide cloud members. Spectroscopic follow-up will confirm the nature of individual objects, better constrain their parameters, and allow an initial mass function to be derived

B̅ →Xsγ in two universal extra dimensions

We calculate the leading order corrections to the [overline B]-->Xsgamma decay in the standard model with two large flat universal extra dimensions. We find that the contributions involving the exchange of Kaluza-Klein modes of the physical scalar field a(kl)[plus-minus] depend logarithmically on the ultraviolet cutoff scale Lambda. We emphasize that all flavor-changing neutral current transitions suffer from this problem. Although the ultraviolet sensitivity weakens the lower bound on the inverse compactification radius 1/R that follows from [overline B]-->Xsgamma, the constraint remains stronger than any other available direct measurement. After performing a careful study of the potential impact of cutoff and higher-order effects, we find 1/R>650 GeV at 95% confidence level if errors are combined in quadrature. Our limit is at variance with the parameter region 1/R<~600 GeV preferred by dark matter constraints

S-particles at their naturalness limits

We draw attention on a particular configuration of supersymmetric particle masses, motivated by naturalness and flavour considerations. All its relevant phenomenological properties for the LHC are described in terms of a few physical parameters, irrespective of the underlying theoretical model. This allows a simple characterization of its main features, useful to define a strategy for its discovery.Comment: 13 pages, 8 figures, added reference

A Near-Infrared L Band Survey of the Young Embedded Cluster NGC 2024

We present the results of the first sensitive L band (3.4 micron) imaging study of the nearby young embedded cluster NGC 2024. Two separate surveys of the cluster were acquired in order to obtain a census of the circumstellar disk fraction in the cluster. From an analysis of the JHKL colors of all sources in our largest area, we find an infrared excess fraction of > 86%. The JHKL colors suggest that the infrared excesses arise in circumstellar disks, indicating that the majority of the sources which formed in the NGC 2024 cluster are currently surrounded by, and likely formed with circumstellar disks. The excess fractions remain very high, within the errors, even at the faintest L magnitudes from our deeper surveys suggesting that disks form around the majority of the stars in very young clusters such as NGC 2024 independent of mass. From comparison with published JHKL observations of Taurus, we find the K - L excess fraction in NGC 2024 to be consistent with a high initial incidence of circumstellar disks in both NGC 2024 and Taurus. Because NGC 2024 represents a region of much higher stellar density than Taurus, this suggests that disks may form around most of the YSOs in star forming regions independent of environment. We find a relatively constant JHKL excess fraction with increasing cluster radius, indicating that the disk fraction is independent of location in the cluster. In contrast, the JHK excess fraction increases rapidly toward the central region of the cluster, and is most likely due to contamination of the K band measurements by bright nebulosity in the central regions of the cluster. We identify 45 candidate protostellar sources in the central regions of the NGC 2024 cluster, and find a lower limit on the protostellar phase of early stellar evolution of 0.4 - 1.4 X 10^5 yr, similar to that in Taurus.Comment: 37 pages, 8 figures, 3 tables, To appear in the Astronomical Journa