Statistics of Core Lifetimes in Numerical Simulations of Turbulent, Magnetically Supercritical Molecular Clouds

We present measurements of the mean dense core lifetimes in numerical simulations of magnetically supercritical, turbulent, isothermal molecular clouds, in order to compare with observational determinations. "Prestellar" lifetimes (given as a function of the mean density within the cores, which in turn is determined by the density threshold n_thr used to define them) are consistent with observationally reported values, ranging from a few to several free-fall times. We also present estimates of the fraction of cores in the "prestellar", "stellar'', and "failed" (those cores that redisperse back into the environment) stages as a function of n_thr. The number ratios are measured indirectly in the simulations due to their resolution limitations. Our approach contains one free parameter, the lifetime of a protostellar object t_yso (Class 0 + Class I stages), which is outside the realm of the simulations. Assuming a value t_yso = 0.46 Myr, we obtain number ratios of starless to stellar cores ranging from 4-5 at n_thr = 1.5 x 10^4 cm^-3 to 1 at n_thr = 1.2 x 10^5 cm^-3, again in good agreement with observational determinations. We also find that the mass in the failed cores is comparable to that in stellar cores at n_thr = 1.5 x 10^4 cm^-3, but becomes negligible at n_thr = 1.2 x 10^5 cm^-3, in agreement with recent observational suggestions that at the latter densities the cores are in general gravitationally dominated. We conclude by noting that the timescale for core contraction and collapse is virtually the same in the subcritical, ambipolar diffusion-mediated model of star formation, in the model of star formation in turbulent supercritical clouds, and in a model intermediate between the previous two, for currently accepted values of the clouds' magnetic criticality.Comment: 25 pages, 8 figures, ApJ accepted. Fig.1 animation is at http://www.astrosmo.unam.mx/~e.vazquez/turbulence/movies/Galvan_etal07/Galvan_etal07.htm

Scanning the critical fluctuations -- application to the phenomenology of the two-dimensional XY-model --

We show how applying field conjugated to the order parameter, may act as a very precise probe to explore the probability distribution function of the order parameter. Using this `magnetic-field scanning' on large-scale numerical simulations of the critical 2D XY-model, we are able to discard the conjectured double-exponential form of the large-magnetization asymptote.Comment: 4 pages, 4 figure

INTEGRAL observation of hard X-ray variability of the TeV binary LS5039 / RX J1826.2-1450

LS 5039/RX J1826.2-1450 is one of the few High Mass X-ray binary systems from which radio and high energy TeV emission has been observed. Moreover, variability of the TeV emission with orbital period was detected. We investigate the hard X-ray (25 - 200keV) spectral and timing properties of the source with the monitoring IBIS/ISGRI instrument on-board the INTEGRAL satellite. We present the analysis of INTEGRAL observations for a total of about 3 Msec exposure time, including both public data and data from the Key Programme. We search for flux and spectral variability related to the orbital phase. The source is observed to emit from 25 up to 200 keV and the emission is concentrated around inferior conjunction. Orbital variability in the hard X-ray band is detected and established to be in phase with the orbitally modulated TeV emission observed with H.E.S.S. For this energy range we determine an average flux for the inferior conjunction phase interval of $(3.54 \pm 2.30) \times 10^{-11}$ erg cm$^{-2}$ s$^{-1}$, and a flux upper limit for the superior conjunction phase interval of $1.45 \times 10^{-11}$ erg cm$^{-2}$ s$^{-1}$ (90% conf. level respectively). The spectrum for the inferior conjunction phase interval follows a power law with an index $\Gamma = 2.0^{+0.2}_{-0.2}$ (90% conf. level).Comment: 4 pages, 4 figures, accepted by A&

H-alpha Emission Variability in the gamma-ray Binary LS I +61 303

LS I +61 303 is an exceptionally rare example of a high mass X-ray binary (HMXB) that also exhibits MeV-TeV emission, making it one of only a handful of "gamma-ray binaries". Here we present H-alpha spectra that show strong variability during the 26.5 day orbital period and over decadal time scales. We detect evidence of a spiral density wave in the Be circumstellar disk over part of the orbit. The H-alpha line profile also exhibits a dramatic emission burst shortly before apastron, observed as a redshifted shoulder in the line profile, as the compact source moves almost directly away from the observer. We investigate several possible origins for this red shoulder, including an accretion disk, mass transfer stream, and a compact pulsar wind nebula that forms via a shock between the Be star's wind and the relativistic pulsar wind.Comment: Accepted to Ap

Matching for Balance, Pairing for Heterogeneity in an Observational Study of the Effectiveness of For-Profit and Not-For-Profit High Schools in Chile

Conventionally, the construction of a pair-matched sample selects treated and control units and pairs them in a single step with a view to balancing observed covariates x and reducing the heterogeneity or dispersion of treated-minus-control response differences, Y. In contrast, the method of cardinality matching developed here first selects the maximum number of units subject to covariate balance constraints and, with a balanced sample for x in hand, then separately pairs the units to minimize heterogeneity in Y. Reduced heterogeneity of pair differences in responses Y is known to reduce sensitivity to unmeasured biases, so one might hope that cardinality matching would succeed at both tasks, balancing x, stabilizing Y. We use cardinality matching in an observational study of the effectiveness of for-profit and not-for-profit private high schools in Chile—a controversial subject in Chile—focusing on students who were in government run primary schools in 2004 but then switched to private high schools. By pairing to minimize heterogeneity in a cardinality match that has balanced covariates, a meaningful reduction in sensitivity to unmeasured biases is obtained

Observations of microquasars with the MAGIC telescope

We report on the results from the observations in very high energy band (VHE, E_gamma > 100GeV) of the black hole X-ray binary (BHXB) Cygnus X-1. The observations were performed with the MAGIC telescope, for a total of 40 hours during 26 nights, spanning the period between June and November 2006. We report on the results of the searches for steady and variable gamma-ray signals, including the first experimental evidence for an intense flare, of duration between 1.5 and 24 hours.Comment: Contribution to the 30th ICRC, Merida Mexico, July 2007 on behalf of the MAGIC Collaboratio

Long-Term Flux Monitoring of LSI +61 303 at 2.25 and 8.3 GHz

LSI +61 303 is an exotic binary system consisting of a ~10 Msun B star and a compact object which is probably a neutron star. The system is associated with the interesting radio source GT0236+610 that exhibits bright radio outbursts with a period of 26.5 days. We report the results of continuous daily radio interferometric observations of GT0236+610 at 2.25 and 8.3 GHz from 1994 January to 1996 February. The observations cover 25 complete (and 3 partial) cycles with multiple observations each day. We detect substantial cycle-to-cycle variability of the radio emission characterized by a rapid onset of the radio flares followed by a more gradual decrease of the emission. We detect a systematic change of the radio spectral index alpha which typically becomes larger than zero at the onset of the radio outbursts. This behavior is suggestive of expansion of material initially optically thick to radio frequencies, indicating either that synchrotron or inverse Compton cooling are important or that the free-free optical depth to the source is rapidly changing. After two years of observations, we see only weak evidence for the proposed 4-year periodic modulation in the peak flux of the outbursts. We observe a secular trend in the outburst phases according the the best published ephemeris. This trend indicates either orbital period evolution, or a drift in outburst orbital phase in response to some other change in the system.Comment: 23 pages, LaTex, 7 figures, to appear in ApJ, v491, Dec 10th issue, for associated info and preprints see http://www.srl.caltech.edu/personnel/paulr/lsi.htm

A radio and infrared exploration of the Cygnus X-3 environments

To confirm, or rule out, the possible hot spot nature of two previously detected radio sources in the vicinity of the Cygnus X-3 microquasar. We present the results of a radio and near infrared exploration of the several arc-minute field around the well known galactic relativistic jet source Cygnus X-3 using the Very Large Array and the Calar Alto 3.5~m telescope. The data this paper is based on do not presently support the hot spot hypothesis. Instead, our new observations suggest that these sources are most likely background or foreground objects. Actually, none of them appears to be even barely extended as would be expected if they were part of a bow shock structure. Our near infrared observations also include a search for extended emission in the Bracket $\gamma$ (2.166 $\mu$m) and $H_{2}$ (2.122 $\mu$m) lines as possible tracers of shocked gas in the Cygnus X-3 surroundings. The results were similarly negative and the corresponding upper limits are reported.Comment: Accepted for publication in A&A; 5 pages, 4 figure

Luminal Ca2+ depletion during the unfolded protein response in Xenopus oocytes: Cause and consequence

The endoplasmic reticulum (ER) is a Ca2+ storing organelle that plays a critical role in the synthesis, folding and post-translational modifications of many proteins. The ER enters into a condition of stress when the load of newly synthesized proteins exceeds its folding and processing capacity. This activates a signal transduction pathway called the unfolded protein response (UPR) that attempts to restore homeostasis. The precise role of ER Ca2+ in the initiation of the UPR has not been defined. Specifically, it has not been established whether ER Ca2+ dysregulation is a cause or consequence of ER stress. Here, we report that partial depletion of ER Ca2+ stores induces a significant induction of the UPR, and leads to the retention of a normally secreted protein Carboxypeptidase Y. Moreover, inhibition of protein glycosylation by tunicamycin rapidly induced an ER Ca2+ leak into the cytosol. However, blockade of the translocon with emetine inhibited the tunicamycin-induced Ca2+ release. Furthermore, emetine treatment blocked elF2α phosphorylation and reduced expression of the chaperone BiP. These findings suggest that Ca2+ may be both a cause and a consequence of ER protein misfolding. Thus, it appears that ER Ca2+ leak is a significant co-factor for the initiation of the UPR.Fil: Paredes, R. Madelaine. University of Texas; Estados UnidosFil: Bollo, Mariana Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigación Médica Mercedes y Martín Ferreyra. Universidad Nacional de Córdoba. Instituto de Investigación Médica Mercedes y Martín Ferreyra; ArgentinaFil: Holstein, Deborah. University of Texas; Estados UnidosFil: Lechleiter, James D.. University of Texas; Estados Unido

Post-eruption morphological evolution and vegetation dynamics of the Blanco River, southern Chile

In this study, we analysed the morphological evolution of a channel segment in the Blanco River in southern Chile that was affected by the Chaitén Volcano eruption occurred in 2008–2009. Through a series of high-resolution satellite images from 2005 to 2019 that represents the entire pre- and post-eruptive dynamics and land covers, we tracked the geomorphological evolution of a 5.65-km-long river segment using channel form indices and also monitored the vegetation dynamics using object-based image analysis (OBIA). Discharge record for the Blanco River was also reconstructed to support the analysis of channel morphologic process. The study aims at examining whether a) the river channel is still adjusting 10 years after the eruption and if so, at what magnitude and, b) the recovered riparian vegetation plays a significant role in stabilising the river streambanks and terraces. We found that even 10 years after the eruption, the Blanco River channel planform is still adjusting, showing a simpler and stable channel configuration in the upstream reaches of the valley, where a certain degree of equilibrium appears to have been attained. More dynamic morphologies were observed in the reaches downstream that have to accommodate the arrival of large amounts of freshly eroded sediments. Our analysis showed that the occurrence of competent floods capable of reworking the river channel matches with the geomorphic indices and mark the post-eruption adjustments of the channel. Finally, the in-channel and riparian vegetation does not play a significant role in stabilising the active channel, streambanks, and terraces, reinforcing the recolonization of sedimentary active areas occurring elsewhere in the valley.This research was developed within the frame of the project FONDECYT 1170413 funded by the Chilean Government. Authors acknowledge the support of the Economy and Knowledge Department of the Catalan Government through the Fluvial Dynamics Research Group (RIUS) SGR017-459