Chandra Reveals Variable Multi-Component X-ray Emission from FU Orionis

FU Orionis is the prototype of a class of eruptive young stars (``FUors'') characterized by strong optical outbursts. We recently completed an exploratory survey of FUors using XMM-Newton to determine their X-ray properties, about which little was previously known. The prototype FU Ori and V1735 Cyg were detected. The X-ray spectrum of FU Ori was found to be unusual, consisting of a cool moderately-absorbed component plus a hotter component viewed through an absorption column density that is an order of magnitude higher. We present here a sensitive (99 ks) follow-up X-ray observation of FU Ori obtained at higher angular resolution with Chandra ACIS-S. The unusual multi-component spectrum is confirmed. The hot component is centered on FU Ori and dominates the emission above 2 keV. It is variable (a signature of magnetic activity) and is probably coronal emission originating close to FU Ori's surface viewed through cool gas in FU Ori's strong wind or accretion stream. In contrast, the X-ray centroid of the soft emission below 2 keV is offset 0.20 arcsec to the southeast of FU Ori, toward the near-IR companion (FU Ori S). This offset amounts to slightly less than half the separation between the two stars. The most likely explanation for the offset is that the companion contributes significantly to the softer X-ray emission below 2 keV (and weakly above 2 keV). The superimposed X-ray contributions from FU Ori and the companion resolve the paradox posed by XMM-Newton of an apparently single X-ray source viewed through two different absorption columns.Comment: 21 pages, 3 tables, 6 figure

Million-Degree Plasma Pervading the Extended Orion Nebula

Most stars form as members of large associations within dense, very cold (10 to 100 kelvin) molecular clouds. The nearby giant molecular cloud in Orion hosts several thousand stars of ages less than a few million years, many of which are located in or around the famous Orion Nebula, a prominent gas structure illuminated and ionized by a small group of massive stars (the Trapezium). We present x-ray observations obtained with the X-ray Multi-Mirror satellite XMM-Newton, revealing that a hot plasma with a temperature of 1.7 to 2.1 million kelvin pervades the southwest extension of the nebula. The plasma flows into the adjacent interstellar medium. This x-ray outflow phenomenon must be widespread throughout our Galaxy

Discovery of a New Soft Gamma Repeater, SGR 1627-41

We report the discovery of a new soft gamma repeater (SGR), SGR 1627-41, and present BATSE observations of the burst emission and BeppoSAX NFI observations of the probable persistent X-ray counterpart to this SGR. All but one burst spectrum are well fit by an optically thin thermal bremsstrahlung (OTTB) model with kT values between 25 and 35 keV. The spectrum of the X-ray counterpart, SAX J1635.8-4736, is similar to that of other persistent SGR X-ray counterparts. We find weak evidence for a periodic signal at 6.41 s in the light curve for this source. Like other SGRs, this source appears to be associated with a young supernova remnant G337.0-0.1. Based upon the peak luminosities of bursts observed from this SGR, we find a lower limit on the dipole magnetic field of the neutron star B_dipole > 5 * 10^14 Gauss.Comment: 5 pages, 4 figures, submitted to ApJ Letter

X-ray Emission from the FU Orionis Star V1735 Cygni

The variable star V1735 Cyg (= Elias 1-12) lies in the IC 5146 dark cloud and is a member of the class of FU Orionis objects whose dramatic optical brightenings are thought to be linked to episodic accretion. We report the first X-ray detections of V1735 Cyg and a deeply-embedded class I protostar lying 24 arcsecs to its northeast. X-ray spectra obtained with EPIC on XMM-Newton reveal very high-temperature plasma (kT > 5 keV) in both objects, but no large flares. Such hard X-ray emission is not anticipated from accretion shocks and is a signature of magnetic processes. We place these new results into the context of what is presently known about the X-ray properties of FU Orionis stars and other accreting young stellar objects.Comment: 25 pages, 6 figure

Effects of macrofauna on acoustic backscatter from the seabed: Field manipulations in West Sound, Orcas Island, Washington, U.S.A.

Previous observations with a bottom-mounted, radially scanning sonar (BAMS) at 40 kHz suggested that macrofaunal activities influence low-angle, acoustic backscatter from seafloor sediments. In order to test that possibility experimentally, we measured and modeled time series of backscatter strength at both 40 and 300 kHz prior to manipulation and then introduced several macrofaunal species at known abundances to randomly selected locations within the ensonified area. We worked in West Sound, Orcas Island, Washington, at a water depth of 20.4 m and for the more frequently recorded 40-kHz series extracted effects by the time-series method known as intervention analysis, wherein the intervention was the experimental alteration. We observed increased backscatter from patches of the small protobranch bivalve Acila castrensis, and of the cockle Clinocardium nuttali, from bait used as chum for fishes and crabs, and from tethered crabs (Cancer magister); other treatments showed no significant change. All of the effective treatments involved increased backscatter at 300 kHz from animals that have obvious hard parts or air bladders. Power calculations for intervention analysis and geoacoustic modeling suggest that failure of other treatments to show significant effects on backscatter strength stems from the small size of the organisms and structures used relative to the 40-kHz wavelength (3.7 cm) and to low sound-speed contrasts between surficial sediments at this site and overlying water (at both frequencies), producing low backscatter levels from both volume heterogeneity and surface microtopography. This experiment demonstrates, however, that low-angle acoustic backscatter can be used to observe at least some populations of benthic animals over a large area (ca. 8000 m2) and that intervention analysis can be a useful tool where logistics permit repeated observation but few or no spatial replicates—frequently the case in ecological manipulations

The Unusual X-ray Spectrum of FU Orionis

FU Orionis stars (FUors) are young low-mass eruptive stars that are thought to be accreting at high rates. They could give rise to soft X-ray emission from accretion shocks, but their X-ray properties are largely unknown. We report the first X-ray detection of the prototype star FU Orionis with XMM-Newton. Its X-ray spectrum is unusual compared to those of classical T Tauri stars (cTTS). The cool and hot components typically detected in cTTS are present but are seen through different absorption column densities. A heavily-absorbed hot component at kT > 5 keV accounts for most of the observed flux and a strong Fe K emission line is present. Such high temperatures are characteristic of magnetic processes rather than shock emission. We discuss possible origins of the unusual spectrum in the context of a complex physical environment that likely includes disk accretion, a strong wind, magnetic activity, and close binarity.Comment: ApJ, vol. 643, in press. 23 pages, 4 figures, 1 tabl

Effectiveness of GonaCon as an immunocontraceptive in colony-housed cats

Objectives Non-surgical contraceptive management of free-roaming cat populations is a global goal for public health and humane reasons. The objectives of this study were to measure the duration of contraception following a single intramuscular injection of a gonadotropin-releasing hormone-based vaccine (GonaCon) and to confirm its safe use in female cats living in colony conditions. Methods GonaCon (0.5 ml/cat) was administered intramuscularly to 20 intact female cats (queens), and saline was administered to 10 queens serving as sham-treated controls. Beginning in late February, 4 months after injection, all cats were housed with fertile male cats in a simulated colony environment. Time to pregnancy, fetal counts and vaccine-elicited injection-site reactions were evaluated. Results All control cats (n = 10/10) and 60% (n = 12/20) of vaccinated cats became pregnant within 4 months of the introduction of males. Two additional vaccinates became pregnant (70%; n = 14/20) within 1 year of treatment. Average fetal counts were significantly lower in vaccinated cats than in control cats. Vaccinates had a significantly longer (P = 0.0120) median time to conception (212 days) compared with controls (127.5 days). Injection-site reactions ranging from swelling to transient granulomatous masses were observed in 45% (n = 9/20) of vaccinated cats. Conclusions and relevance A single dose of GonaCon provided contraception lasting for a minimum of 1 year in 30% (n = 6/20) of treated cats. The level of contraception induced by this GonaCon dose and vaccine lot was not sufficiently effective to be recommended for use in free-roaming cats

Effectiveness of GonaCon as an immunocontraceptive in colony-housed cats

Objectives Non-surgical contraceptive management of free-roaming cat populations is a global goal for public health and humane reasons. The objectives of this study were to measure the duration of contraception following a single intramuscular injection of a gonadotropin-releasing hormone-based vaccine (GonaCon) and to confirm its safe use in female cats living in colony conditions. Methods GonaCon (0.5 ml/cat) was administered intramuscularly to 20 intact female cats (queens), and saline was administered to 10 queens serving as sham-treated controls. Beginning in late February, 4 months after injection, all cats were housed with fertile male cats in a simulated colony environment. Time to pregnancy, fetal counts and vaccine-elicited injection-site reactions were evaluated. Results All control cats (n = 10/10) and 60% (n = 12/20) of vaccinated cats became pregnant within 4 months of the introduction of males. Two additional vaccinates became pregnant (70%; n = 14/20) within 1 year of treatment. Average fetal counts were significantly lower in vaccinated cats than in control cats. Vaccinates had a significantly longer (P = 0.0120) median time to conception (212 days) compared with controls (127.5 days). Injection-site reactions ranging from swelling to transient granulomatous masses were observed in 45% (n = 9/20) of vaccinated cats. Conclusions and relevance A single dose of GonaCon provided contraception lasting for a minimum of 1 year in 30% (n = 6/20) of treated cats. The level of contraception induced by this GonaCon dose and vaccine lot was not sufficiently effective to be recommended for use in free-roaming cats

Charge-charge interactions are key determinants of the pK values of ionizable groups in ribonuclease Sa (pI=3.5) and a basic variant (pI=10.2)

The pK values of the titratable groups in ribonuclease Sa (RNase Sa) (pI=3.5), and a charge-reversed variant with five carboxyl to lysine substitutions, 5K RNase Sa (pI=10.2), have been determined by NMR at 20 °C in 0.1 M NaCl. In RNase Sa, 18 pK values and in 5K, 11 pK values were measured. The carboxyl group of Asp33, which is buried and forms three intramolecular hydrogen bonds in RNase Sa, has the lowest pK (2.4), whereas Asp79, which is also buried but does not form hydrogen bonds, has the most elevated pK (7.4). These results highlight the importance of desolvation and charge–dipole interactions in perturbing pK values of buried groups. Alkaline titration revealed that the terminal amine of RNase Sa and all eight tyrosine residues have significantly increased pK values relative to model compounds. A primary objective in this study was to investigate the influence of charge–charge interactions on the pK values by comparing results from RNase Sa with those from the 5K variant. The solution structures of the two proteins are very similar as revealed by NMR and other spectroscopic data, with only small changes at the N terminus and in the α-helix. Consequently, the ionizable groups will have similar environments in the two variants and desolvation and charge–dipole interactions will have comparable effects on the pK values of both. Their pK differences, therefore, are expected to be chiefly due to the different charge–charge interactions. As anticipated from its higher net charge, all measured pK values in 5K RNase are lowered relative to wild-type RNase Sa, with the largest decrease being 2.2 pH units for Glu14. The pK differences (pKSa−pK5K) calculated using a simple model based on Coulomb's Law and a dielectric constant of 45 agree well with the experimental values. This demonstrates that the pK differences between wild-type and 5K RNase Sa are mainly due to changes in the electrostatic interactions between the ionizable groups. pK values calculated using Coulomb's Law also showed a good correlation (R=0.83) with experimental values. The more complex model based on a finite-difference solution to the Poisson–Boltzmann equation, which considers desolvation and charge–dipole interactions in addition to charge–charge interactions, was also used to calculate pK values. Surprisingly, these values are more poorly correlated (R=0.65) with the values from experiment. Taken together, the results are evidence that charge–charge interactions are the chief perturbant of the pK values of ionizable groups on the protein surface, which is where the majority of the ionizable groups are positioned in proteins.This work was supported by grants GM-37039 and GM-52483 from the National Institutes of Health (USA), grants BE-1060 and BE-1281 from the Robert A. Welch Foundation, and a grant PB-93-06777 to M.R. from the Dirección General de Investigación Cientı́fica y Técnica (Spain