Modulations in Multi-Periodic Blue Variables in the LMC

As shown by Mennickent, et al(2003), a subset of the blue variable stars in the Large Magellanic Cloud exhibit brightness variability of small amplitude in the period range 2.4 to 16 days as well as larger amplitude variability with periods of 140 to 600 days, with a remarkably tight relation between the long and the short periods. Our re-examination of these objects has led to the discovery of additional variability. The Fourier spectra of 11 of their 30 objects have 3 or 4 peaks above the noise level and a linear relation of the form f_a = 2(f_b - f_L) among three of the frequencies. An explanation of this relation requires an interplay between the binary motion and that of a third object. The two frequency relations together with the Fourier amplitude ratios pose a challenging modeling problem.Comment: 4 pages, 3 figures, Astrophysical Journal (in press

The nature of the progenitor of the Type II-P supernova 1999em

We present high quality ground-based VRI images of the site of the Type II-P SN1999em (in NGC1637) taken before explosion, which were extracted from the CFHT archive. We determine a precise position of the SN on these images to an accuracy of 0.17''. The host galaxy is close enough (7.5 +/- 0.5 Mpc) that the bright supergiants are resolved as individual objects, however we show that there is no detection of an object at the SN position before explosion that could be interpreted as the progenitor star. By determining the sensitivity limits of the VRI data, we derive bolometric luminosity limits for the progenitor. Comparing these to standard stellar evolutionary tracks which trace evolution up to the point of core carbon ignition, we initially derive an upper mass limit of approximately 12M_sol. However we present evolutionary calculations that follow 7-12M_sol stars throughout their C-burning lifetime and show that we can restrict the mass of the progenitor even further. Our calculations indicate that progenitors initially of 8-10M_sol, undergoing expected mass loss, can also be excluded because a second dredge up sends them to somewhat higher luminosities than a star of initially 12M_sol. These results limit the progenitor's initial main-sequence mass to a very narrow range of 12 +/- 1 M_sol. We discuss the similarities between the Type II-P SNe 1999em and 1999gi and their progenitor mass limits, and suggest that SN Type II-P originate only in intermediate mass stars of 8-12M_sol, which are in the red supergiant region and that higher mass stars produce the other Type II sub-types. (Abridged).Comment: Replaced with accepted version to appear in ApJ, 30 pages, inc. 6 figure

Extent of pollution in planet-bearing stars

(abridged) Search for planets around main-sequence (MS) stars more massive than the Sun is hindered by their hot and rapidly spinning atmospheres. This obstacle has been sidestepped by radial-velocity surveys of those stars on their post-MS evolutionary track (G sub-giant and giant stars). Preliminary observational findings suggest a deficiency of short-period hot Jupiters around the observed post MS stars, although the total fraction of them with known planets appears to increase with their mass. Here we consider the possibility that some very close- in gas giants or a population of rocky planets may have either undergone orbital decay or been engulfed by the expanding envelope of their intermediate-mass host stars. If such events occur during or shortly after those stars' main sequence evolution when their convection zone remains relatively shallow, their surface metallicity can be significantly enhanced by the consumption of one or more gas giants. We show that stars with enriched veneer and lower-metallicity interior follow slightly modified evolution tracks as those with the same high surface and interior metallicity. As an example, we consider HD149026, a marginal post MS 1.3 Msun star. We suggest that its observed high (nearly twice solar) metallicity may be confined to the surface layer as a consequence of pollution by the accretion of either a planet similar to its known 2.7-day-period Saturn-mass planet, which has a 70 Mearth compact core, or a population of smaller mass planets with a comparable total amount of heavy elements. It is shown that an enhancement in surface metallicity leads to a reduction in effective temperature, in increase in radius and a net decrease in luminosity. The effects of such an enhancement are not negligible in the determinations of the planet's radius based on the transit light curves.Comment: 25 pages, 8 figures, submitted to Ap

Binary coalescence from case A evolution -- mergers and blue stragglers

We constructed some main-sequence mergers from case A binary evolution and studied their characteristics via Eggleton's stellar evolution code. Both total mass and orbital angular momentum are conservative in our binary evolutions. Some mergers might be on the left of the ZAMS as defined by normal surface composition on a CMD because of enhanced surface helium content. The study also shows that central hydrogen content of the mergers is independent of mass. As a consequence, we fit the formula of magnitude and B-V of the mergers when they return back to thermal equilibrium with maximum error 0.29 and 0.037, respectively. Employing the consequences above, we performed Monte Carlo simulations to examine our models in NGC 2682 and NGC 2660. In NGC 2682, binary mergers from our models cover the region with high luminosity, but its importance is much less than that of AML. Our results are well-matched to the observations of NGC2660 if there is about 0.5Mo of mass loss in the merger process.Comment: 14 pages, 12 figures. accepted by MNRA

Alignment Timescale of the Microquasar GRO J1655-40

The microquasar GRO J1655-40 has a black hole with spin angular momentum apparently misaligned to the orbital plane of its companion star. We analytically model the system with a steady state disc warped by Lense-Thirring precession and find the timescale for the alignment of the black hole with the binary orbit. We make detailed stellar evolution models so as to estimate the accretion rate and the lifetime of the system in this state. The secondary can be evolving at the end of the main sequence or across the Hertzsprung gap. The mass-transfer rate is typically fifty times higher in the latter case but we find that, in both cases, the lifetime of the mass transfer state is at most a few times the alignment timescale. The fact that the black hole has not yet aligned with the orbital plane is therefore consistent with either model. We conclude that the system may or may not have been counter-aligned after its supernova kick but that it is most likely to be close to alignment rather than counteralignment now.Comment: Accepted for publication in MNRA

Pullet flock management

Proper feeding and management of the laying flock is the producer’s responsibility. Well fed, healthy flocks, housed in adequate quarters should average 50 to 70 percent production during the entire laying season. If this production is not attained with proper management practices, the flock owner should give more careful consideration to the type of stock being purchased. Rigorous culling several times during the season should be practiced to eliminate the poor layers and those that drop out of production early. Information available from Extension Service, Iowa State College, in bulletin form, will serve as a guide to proper culling techniques. The amount of feed consumed by a flock o f laying hens depends largely on the breed, body size and the rate of production. The feed intake of the hen is used (1) to maintain the body and supply body warmth, (2) to increase body weight and (3) to produce eggs. Flocks in heavy production consume much more feed than those producing only a few eggs. Table 2 may be used as a guide to calculate the yearly feed requirement. The proportion of grain, mash and green feed necessary to make up the yearly diet will vary according to the method of feeding and the amount of protein in the mash. It will be noted that the word ration applies to all the feed elements eaten by the flock from any source

The Evolutionary Status of SS433

We consider possible evolutionary models for SS 433. We assume that common-envelope evolution is avoided if radiation pressure is able to expel most of a super-Eddington accretion flow from a region smaller than the accretor's Roche lobe. This condition is satisfied, at least initially, for largely radiative donors with masses in the range 4-12 solar masses. For donors more massive than about 5 solar masses, moderate mass ratios q = M_2/M_1 > 1 are indicated, thus tending to favor black-hole accretors. For lower mass donors, evolutionary considerations do not distinguish between a neutron star or black hole accretor. In all cases the mass transfer (and mass loss) rates are much larger than the likely mass-loss rate in the precessing jets. Almost all of the transferred mass is expelled at radii considerably larger than the jet acceleration region, producing the "stationary" H-alpha line, the infrared luminosity, and accounting for the low X-ray luminosity.Comment: 13 pages, Astrophysical Journal Letters, accepte

Planet Consumption and Stellar Metallicity Enhancements

The evolution of a giant planet within the stellar envelope of a main-sequence star is investigated as a possible mechanism for enhancing the stellar metallicities of the parent stars of extrasolar planetary systems. Three-dimensional hydrodynamical simulations of a planet subject to impacting stellar matter indicate that the envelope of a Jupiter-like giant planet can be completely stripped in the outer stellar convection zone of a solar-mass star. In contrast, Jupiter-like and less massive Saturn-like giant planets are able to survive through the base of the convection zone of a 1.22 solar-mass star. Although strongly dependent on details of planetary interior models, partial or total dissolution of giant planets can result in significant enhancements in the metallicity of host stars with masses between about 1.0 and 1.3 solar masses. The implications of these results with regard to planetary orbital migration are briefly discussed.Comment: 11 pages, 2 figures, accepted for ApJ Letter

Gap solitons in Bragg gratings with a harmonic superlattice

Solitons are studied in a model of a fiber Bragg grating (BG) whose local reflectivity is subjected to periodic modulation. The superlattice opens an infinite number of new bandgaps in the model's spectrum. Averaging and numerical continuation methods show that each gap gives rise to gap solitons (GSs), including asymmetric and double-humped ones, which are not present without the superlattice.Computation of stability eigenvalues and direct simulation reveal the existence of completely stable families of fundamental GSs filling the new gaps - also at negative frequencies, where the ordinary GSs are unstable. Moving stable GSs with positive and negative effective mass are found too.Comment: 7 pages, 3 figures, submitted to EP

Efficiency of mass transfer in massive close binaries, Tests from double-lined eclipsing binaries in the SMC

One of the major uncertainties in close binary evolution is the efficiency of mass transfer beta: the fraction of transferred mass that is accreted by a secondary star. We attempt to constrain the mass-transfer efficiency for short-period massive binaries undergoing case A mass transfer. We present a grid of about 20,000 detailed binary evolution tracks with primary masses 3.5-35 Msun, orbital periods 1-5 days at a metallicity Z=0.004, assuming both conservative and non-conservative mass transfer. We perform a systematic comparison, using least-squares fitting, of the computed models with a sample of 50 double-lined eclipsing binaries in the Small Magellanic Cloud, for which fundamental stellar parameters have been determined. About 60% of the systems are currently undergoing slow mass transfer. In general we find good agreement between our models and the observed detached systems. However, for many of the semi-detached systems the observed temperature ratio is more extreme than our models predict. For the 17 semi-detached systems that we are able to match, we find a large spread in the best fitting mass-transfer efficiency; no single value of beta can explain all systems. We find a hint that initially wider systems tend to fit better to less conservative models. We show the need for more accurate temperature determinations and we find that determinations of surface abundances of nitrogen and carbon can potentially constrain the mass-transfer efficiency further.Comment: Accepted for publication in A&A 15/03/2007, 16 page