The Distance and Age of the SNR Kes 73 and AXP 1E 1841-045

We provide a new distance estimate to the supernova remnant (SNR) Kes 73 and its associated anomalous X-ray pulsar (AXP) 1E 1841-045. 21 cm HI images and HI absorption/ emission spectra from new VLA observations, and 13CO emission spectra of Kes 73 and two adjacent compact HII regions (G27.276+0.148 and G27.491+0.189) are analyzed. The HI images show prominent absorption features associated with Kes 73 and the HII regions. The absorption appears up to the tangent point velocity giving a lower distance limit to Kes 73 of 7.5 kpc, which has previously been given as the upper limit. Also, G27.276+0.148 and G27.491+0.189 are at the far kinematic distances of their radio recombination line velocities. There is prominent HI emission in the range 80--90 km/s for all three objects. The two HII regions show HI absorption at ~ 84 km/s, but there is no absorption in the Kes 73 absorption spectrum. This implies an upper distance limit of ~ 9.8 kpc to Kes 73. This corrected larger distance to Kes 73/ AXP 1E 1841-045 system leads to a refined age of the SNR of 500 to 1000 yr, and a ~ 50% larger AXP X-ray luminosity.Comment: 10 pages, 2 figures, ApJ, dol:10.1086/"529120

Systematics of fusion probability in "hot" fusion reactions

The fusion probability in "hot" fusion reactions leading to the synthesis of super-heavy nuclei is investigated systematically. The quasi-fission barrier influences the formation of the super-heavy nucleus around the "island of stability" in addition to the shell correction. Based on the quasi-fission barrier height obtained with the Skyrme energy-density functional, we propose an analytical expression for the description of the fusion probability, with which the measured evaporation residual cross sections can be reproduced acceptably well. Simultaneously, some special fusion reactions for synthesizing new elements 119 and 120 are studied. The predicted evaporation residual cross sections for 50Ti+249Bk are about 10-150fb at energies around the entrance-channel Coulomb barrier. For the fusion reactions synthesizing element 120 with projectiles 54Cr and 58Fe, the cross sections fall to a few femtobarns which seems beyond the limit of the available facilities.Comment: 5 figures, 1 tabl

How does the stellar wind influence the radio morphology of a supernova remnant?

We simulate the evolutions of the stellar wind and the supernova remnant (SNR) originating from a runaway massive star in an uniform Galactic environment based on the three-dimensional magnetohydrodynamics models. Taking the stellar wind into consideration, we can explain the radio morphologies of many supernova remnants. The directions of the kinematic velocity of the progenitor, the magnetic field and the line of sight are the most important factors influencing the morphologies. If the velocity is perpendicular to the magnetic field, the simulation will give us two different unilateral SNRs and a bilateral symmetric SNR. If the velocity is parallel to the magnetic field, we can obtain a bilateral asymmetric SNR and a quasi-circular SNR. Our simulations show the stellar wind plays a key role in the radio evolution of a SNR, which implies the Galactic global density and magnetic field distribution play a secondary role in shaping a SNR.Comment: 12pages, 35 figures, accepted for publication in Ap

The HI absorption distance of HESS J1943+213 favours its extragalactic nature

The H.E.S.S. collaboration (Abramowski et al. 2011) dicovered a new TeV point-like source HESS J1943+213 in the Galactic plane and suggested three possible low-energy-band counterparts: a $\gamma$-ray binary, a pulsar wind nebula (PWN), or a BL Lacertae object. We measure the distance to the radio counterpart G57.76-1.29 of HESS J1943+213. We analyze Very Large Array observations to obtain a reliable HI absorption spectrum.The resulting distance limit is $\ge$ 16 kpc. This distance strongly supports that HESS J1943+213 is an extragalactic source, consistent with the preferred counterpart of the HESS collaboration.Comment: 3 figures, 2 pages, A&A accepte

Precise Ages of Field Stars from White Dwarf Companions

Observational tests of stellar and Galactic chemical evolution call for the joint knowledge of a star's physical parameters, detailed element abundances, and precise age. For cool main-sequence (MS) stars the abundances of many elements can be measured from spectroscopy, but ages are very hard to determine. The situation is different if the MS star has a white dwarf (WD) companion and a known distance, as the age of such a binary system can then be determined precisely from the photometric properties of the cooling WD. As a pilot study for obtaining precise age determinations of field MS stars, we identify nearly one hundred candidates for such wide binary systems: a faint WD whose GPS1 proper motion matches that of a brighter MS star in Gaia/TGAS with a good parallax ($\sigma_\varpi/\varpi\le 0.05$). We model the WD's multi-band photometry with the BASE-9 code using this precise distance (assumed to be common for the pair) and infer ages for each binary system. The resulting age estimates are precise to $\le 10\%$ ($\le 20\%$) for $42$ ($67$) MS-WD systems. Our analysis more than doubles the number of MS-WD systems with precise distances known to date, and it boosts the number of such systems with precise age determination by an order of magnitude. With the advent of the Gaia DR2 data, this approach will be applicable to a far larger sample, providing ages for many MS stars (that can yield detailed abundances for over 20 elements), especially in the age range 2 to 8\,\Gyr, where there are only few known star clusters.Comment: 9 pages, 5 figures, 1 catalog; Submitted to Ap