No abstract

We show that many observations of W44, a supernova remnant in the Galactic plane at a distance of about 2500 pc, are remarkably consistent with the simplest realistic model. The model remnant is evolving in a smooth ambient medium of fairly high density, about 6 cm~3 on average, with a substantial density gradient. At the observed time it has an age of about 20,000 yr, consistent with the age of the associated pulsar, and a radius of 11È13 pc. Over most of the outer surface, radiative cooling has become important in the postshock gas ; on the denser end there has been sufficient compression of the cooled gas to develop a very thin dense half-shell of about 450 supported against further compression by M _ , nonthermal pressure. The half-shell has an expansion velocity of about 150 km s~1 and is bounded on the outer surface by a radiative shock with that speed. The deep interior of the remnant has a substantial and fairly uniform pressure, as expected from even highly idealized adiabatic models ; our model, however, is never adiabatic. Thermal conduction, while the remnant is young and hot, reduces the need for expansion cooling and prevents formation of the intensely vacuous cavity characteristic of adiabatic evolution. It radically alters the interior structure from what one might expect from familiarity with the Sedov solution. At the time of observation, the temperature in the center is about 6 ] 106 K, the density about 1 cm~3. The temperature decreases gradually away from the center, while the density rises. Farther out, where cooling is becoming important, the pressure drops precipitously, and the temperature in the denser gas there is quite low. We provide several analytic tools for the assembly of models of this type. We review the early evolution and shell formation analyses and their generalizations to evolution in a density gradient. We also calculate the density and temperature that should be present in the hot interior of a remnant with thermal conduction. We supply the van der Laan mechanism in a particularly useful form for the calculation of radio continuum from radiative remnants. Finally, we estimate the optical emission that should be present from Ñuorescence of UV light, emitted by the forming shell and the radiative shock and absorbed in the cold shell and the ambient medium, and the associated 63 km [O I] emission. Both are in agreement with the intensity and spatial structures found in recent observations. Neither requires interaction with a dense molecular cloud for its generation. We calculate the gamma rays that should be emitted by cosmic-ray electrons and ions in the shell, interacting with the cold material, and Ðnd each capable of generating about 25% of the Ñux reported by EGRET for the vicinity.

We present frequency analysis of RR Lyrae stars of globular cluster NGC 6362. 1 Observations and data analysis NGC 6362 is a nearby globular cluster of Oosterhoff I type. It has a mean metallicity of [Fe/H]= −0.95 and belongs to the old halo population ([1]). 35 RR Lyrae-type stars have been discovered in the cluster ([5]). We revisit these variables, taking advantage of the new CCD photometry accumulated by the Cluster AgeS Experiment (CASE). In our analysis we used 3200 V-band images collected with the 1-m Swope telescope of the Las Campanas Observatory between July 8th, 1999 and September 9th, 2009. The frequency analysis of the data was performed with the standard consecutive prewhitening technique. For full discussion of our results we refer the reader to [6]. 2 RR Lyrae variables of NGC 6362 16 RR Lyrae stars of NGC 6362 are fundamental mode pulsators (RRab variables) and 16 are first overtone pulsators (RRc variables). Two objects, previously identified as RRab stars, turned out to be double mode pulsators (RRd stars), with two lowest radial modes simultaneously excited. Finally, in V37 we detect two high-amplitude modes of close frequencies and with lightcurves significantly differing from those of RR Lyrae stars. The nature of V37 is a puzzle. It will not be discussed here. 2.1 Non-radial modes In 10 out of 16 RRc stars of NGC 6362 (63% of the sample) we detect a secondary short period variability, with the period ratio falling in the range of P x /P 1 = 0.60 − 0.65. The amplitudes of the secondary signals never exceed 6 mmag. Similar pulsators have recently been discovered in many stellar systems ([3], and references therein). Space observations indicate that this form of variability most likely occurs in almost all RRc and RRd stars ([4]). Detecting it in the ground-based data is difficult, however, because of the extremely low amplitude of the secondary periodicities. The incidence rate of 63%, that we report for NGC 6362, is the highest among all stellar systems observed

We show that many observations of W44, a supernova remnant in the galactic plane at a distance of about 2500 pc, are remarkably consistent with the simplest realistic model. The model remnant is evolving in a smooth ambient medium of fairly high density, about 6 cm −3 on average, with a substantial density gradient. At the observed time it has an age of about 20,000 years, consistent with the age of the associated pulsar, and a radius of 11 to 13 pc. Over most of the outer surface, radiative cooling has become important in the post shock gas; on the denser end there has been sufficient compression of the cooled gas to develop a very thin dense half shell of about 450 M⊙ , supported against further compression by nonthermal pressure. The half shell has an expansion velocity of about 150 km s −1 , and is bounded on the outer surface by a radiative shock with that speed.The deep interior of the remnant has a substantial and fairly uniform pressure, as expected from even highly idealized adiabatic models; our model, however, is never adiabatic. Thermal conduction, while the remnant is young and hot, reduces the need for expansion cooling, and prevents formation of the intensely vacuous cavity characteristic of adiabatic evolution. It radically alters the interior structure from what one might expect from familiarity with the Sedov solution. At the time of observation, the temperature in the center is about 6×10 6 K, the density about 1 cm −3 . The temperature decreases gradually away from the center, while the density rises. Farther out where cooling is becoming important, the pressure drops precipitously and the temperature in the denser gas there is quite low. Our model is similar to but more comprehensive than the recent one by Harrus et al. (1997). Because their model lacked thermal conduction, ours is more successful in providing the thermal x-rays from the hot interior, including a better match to the spectrum, but neither provides the sharpness of the central peaking without further complications.By using a 2d hydrocode to follow the evolution in a density gradient, we are able to verify that the spatial and velocity structure of the HI shell are a good match to the observations, without the complications suggested by Koo and Heiles (1995), and to demonstrate that the remnant's asymmetry does not substantially affect the distribution of x-ray emitting material. A 1d hydrocode model is then used to explore the effects of nonequilibrium ionization on the x-ray spectrum and intensity. We calculate the radio continuum emission expected from the compression of the ambient magnetic field and cosmic rays into the dense shell (the van der Laan mechanism, 1962a) and find it to be roughly consistent with observation, though the required density of ambient cosmic ray electrons is about 4 times greater than that estimated for the solar neighborhood. We estimate the optical emission that should be present from fluorescence of UV, emitted by the forming shell and the radiative shock and absorbed in the cold shell and the am...