Search results for "010303 astronomy & astrophysics"
showing 10 items of 1094 documents
On the timing properties of SAX J1808.4-3658 during its 2015 outburst
2017
We present a timing analysis of the 2015 outburst of the accreting millisecond X-ray pulsar SAX J1808.4-3658, using non-simultaneous XMM-Newton and NuStar observations. We estimate the pulsar spin frequency and update the system orbital solution. Combining the average spin frequency from the previous observed, we confirm the long-term spin down at an average rate $\dot{\nu}_{\text{SD}}=1.5(2)\times 10^{-15}$ Hz s$^{-1}$. We also discuss possible corrections to the spin down rate accounting for mass accretion onto the compact object when the system is X-ray active. Finally, combining the updated ephemerides with those of the previous outbursts, we find a long-term orbital evolution compatibl…
The planar two-body problem for spheroids and disks
2021
We outline a new method suggested by Conway (2016) for solving the two-body problem for solid bodies of spheroidal or ellipsoidal shape. The method is based on integrating the gravitational potential of one body over the surface of the other body. When the gravitational potential can be analytically expressed (as for spheroids or ellipsoids), the gravitational force and mutual gravitational potential can be formulated as a surface integral instead of a volume integral, and solved numerically. If the two bodies are infinitely thin disks, the surface integral has an analytical solution. The method is exact as the force and mutual potential appear in closed-form expressions, and does not invol…
A stellar flare-coronal mass ejection event revealed by X-ray plasma motions
2019
Coronal mass ejections (CMEs), often associated with flares, are the most powerful magnetic phenomena occurring on the Sun. Stars show magnetic activity levels up to 10^4 times higher, and CME effects on stellar physics and circumstellar environments are predicted to be significant. However, stellar CMEs remain observationally unexplored. Using time-resolved high-resolution X-ray spectroscopy of a stellar flare on the active star HR 9024 observed with Chandra/HETGS, we distinctly detected Doppler shifts in S XVI, Si XIV, and Mg XII lines that indicate upward and downward motions of hot plasmas (~10-25 MK) within the flaring loop, with velocity v~100-400 km/s, in agreement with a model of fl…
Evolutionary paths of binaries with a neutron star - I. The case of SAX J1808.4 - 3658
2018
The evolutionary status of the low mass X-ray binary SAX J1808.4-3658 is simulated by following the binary evolution of its possible progenitor system through mass transfer, starting at a period of $\sim$6.6 hr. The evolution includes angular momentum losses via magnetic braking and gravitational radiation. It also takes into account the effects of illumination of the donor by both the X-ray emission and the spin down luminosity of the pulsar. The system goes through stages of mass transfer and stages during which it is detached, where only the rotationally powered pulsar irradiates the donor. We show that the pulsar irradiation is a necessary ingredient to reach SAX J1808.4-3658 orbital pe…
The search for Muon neutrinos from northern hemisphere gamma-ray bursts with AMANDA
2007
We present the results of the analysis of neutrino observations by the Antarctic Muon and Neutrino Detector Array (AMANDA) correlated with photon observations of more than 400 gamma-ray bursts (GRBs) in the Northern Hemisphere from 1997 to 2003. During this time period, AMANDA's effective collection area for muon neutrinos was larger than that of any other existing detector. Based on our observations of zero neutrinos during and immediately prior to the GRBs in the dataset, we set the most stringent upper limit on muon neutrino emission correlated with gamma-ray bursts. Assuming a Waxman-Bahcall spectrum and incorporating all systematic uncertainties, our flux upper limit has a normalizatio…
Fragmentation of anthracene C14H10, acridine C13H9N and phenazine C12H8N2 ions in collisions with atoms
2014
International audience; We report experimental total, absolute, fragmentation cross sections for anthracene C14H10, acridine C13H9N, and phenazine C12H8N2 ions colliding with He at center-of-mass energies close to 100 eV. In addition, we report results for the same ions colliding with Ne, Ar, and Xe at higher energies. The total fragmentation cross sections for these three ions are the same within error bars for a given target. The measured fragment mass distributions reveal significant contributions from both delayed (≫10−12 s) statistical fragmentation processes as well as non-statistical, prompt (∼10−15 s), single atom knockout processes. The latter dominate and are often followed by sec…
Orbital chronology of the lower-middle Aptian: palaeoenvironmental implications (Serre Chaitieu section, Vocontian Basin).
2013
4 pages; International audience; A detailed cyclostratigraphic study conducted on several proxies including spectral gamma ray, magnetic susceptibility, clay minerals, and carbonate content suggests that the return to equilibrium in the carbon cycle after the major disturbance linked with Oceanic Anoxic Event 1a occurred in about 2 Myr. The minimum duration of the D. furcata zone is estimated at 0.46 Myr and that of the E. subnodosocostatum zone at 1.45 Myr. Strengthening of the obliquity record in the furcata zone confirms the cooling that characterizes this period.
H-2, H-3(+) and the age of molecular clouds and prestellar cores
2012
Measuring the age of molecular clouds and prestellar cores is a difficult task that has not yet been successfully accomplished although the information is of paramount importance to help in understanding and discriminating between different formation scenarios. Most chemical clocks suffer from unknown initial conditions and are therefore difficult to use. We propose a new approach based on a subset of deuterium chemistry that takes place in the gas phase and for which initial conditions are relatively well known. It relies primarily on the conversion of H 3 + into H 2D + to initiate deuterium enrichment of the molecular gas. This conversion is controlled by the ortho/para ratio of H2 that i…
Oxygen depletion in dense molecular clouds: a clue to a low O2 abundance?
2011
Context: Dark cloud chemical models usually predict large amounts of O2, often above observational limits. Aims: We investigate the reason for this discrepancy from a theoretical point of view, inspired by the studies of Jenkins and Whittet on oxygen depletion. Methods: We use the gas-grain code Nautilus with an up-to-date gas-phase network to study the sensitivity of the molecular oxygen abundance to the oxygen elemental abundance. We use the rate coefficient for the reaction O + OH at 10 K recommended by the KIDA (KInetic Database for Astrochemistry) experts. Results: The updates of rate coefficients and branching ratios of the reactions of our gas-phase chemical network, especially N + C…
The hyperfine structure in the rotational spectrum of CF+
2012
Context. CF+ has recently been detected in the Horsehead and Orion Bar photo-dissociation regions. The J=1-0 line in the Horsehead is double-peaked in contrast to other millimeter lines. The origin of this double-peak profile may be kinematic or spectroscopic. Aims. We investigate the effect of hyperfine interactions due to the fluorine nucleus in CF+ on the rotational transitions. Methods. We compute the fluorine spin rotation constant of CF+ using high-level quantum chemical methods and determine the relative positions and intensities of each hyperfine component. This information is used to fit the theoretical hyperfine components to the observed CF+ line profiles, thereby employing the h…