Adult and Larval Stomatopod Crustaceans Occurring in Hawaiian Waters

Volume: 7Start Page: 399End Page: 43

Mitigating Charge Transfer Inefficiency in the Chandra X-ray Observatory's ACIS Instrument

The ACIS front-illuminated CCDs onboard the Chandra X-ray Observatory were damaged in the extreme environment of the Earth's radiation belts, resulting in enhanced charge transfer inefficiency (CTI). This produces a row dependence in gain, event grade, and energy resolution. We model the CTI as a function of input photon energy, including the effects of de-trapping (charge trailing), shielding within an event (charge in the leading pixels of the 3X3 event island protect the rest of the island by filling traps), and non-uniform spatial distribution of traps. This technique cannot fully recover the degraded energy resolution, but it reduces the position dependence of gain and grade distributions. By correcting the grade distributions as well as the event amplitudes, we can improve the instrument's quantum efficiency. We outline our model for CTI correction and discuss how the corrector can improve astrophysical results derived from ACIS data.Comment: Accepted by ApJ Letters; see http://www.astro.psu.edu/users/townsley/cti

Structure and Feedback in 30 Doradus I: Observations

We have completed a a new optical imaging and spectrophotometric survey of a 140 x 80 pc$^2$ region of 30 Doradus centered on R136, covering key optical diagnostic emission lines including \Ha, \Hb, \Hg, [O III] $\lambda\lambda$4363, 4959, 5007, [N II] $\lambda\lambda$6548, 6584, [S II] $\lambda\lambda$6717, 6731 [S III] $\lambda$6312 and in some locations [S III] $\lambda$9069. We present maps of fluxes and intensity ratios for these lines, and catalogs of isolated ionizing stars, elephant-trunk pillars, and edge-on ionization fronts. The final science-quality spectroscopic data products are available to the public. Our analysis of the new data finds that, while stellar winds and supernovae undoubtedly produce shocks and are responsible for shaping the nebula, there are no global spectral signatures to indicate that shocks are currently an important source of ionization. We conclude that the considerable region covered by our survey is well described by photoionization from the central cluster where the ionizing continuum is dominated by the most massive O stars. We show that if 30 Dor were viewed at a cosmological distance, its integrated light would be dominated by its extensive regions of lower surface-brightness rather than by the bright, eye-catching arcs.Comment: 42 pages, 16 figures, Accepted for publication in ApJ

The Poultry Club I

Cooperative Extension Work in Agriculture and Home Economics, University of Missouri, College of Agriculture and the United States Department of Agriculture cooperating."March, 1923."Title from cover

Evidence for the White Dwarf Nature of Mira B

The nature of the accreting companion to Mira --- the prototypical pulsating asymptotic giant branch star --- has been a matter of debate for more than 25 years. Here we use a quantitative analysis of the rapid optical brightness variations from this companion, Mira B, which we observed with the Nickel telescope at Lick Observatory, to show that it is a white dwarf (WD). The amplitude of aperiodic optical variations on time scales of minutes to tens of minutes (approximately 0.2 mag) is consistent with that of accreting WDs in cataclysmic variables on these same time scales. It is significantly greater than that expected from an accreting main-sequence star. With Mira B identified as a WD, its ultraviolet (UV) and optical luminosities, along with constraints on the WD effective temperature from the UV, indicate that it accretes at ~1e-10 solar masses per year. We do not find any evidence that the accretion rate is higher than predicted by Bondi-Hoyle theory. The accretion rate is high enough, however, to explain the weak X-ray emission, since the accretion-disk boundary layer around a low-mass WD accreting at this rate is likely to be optically thick and therefore to emit primarily in the far or extreme UV. Furthermore, the finding that Mira B is a WD means that it has experienced, and will continue to experience nova explosions, roughly every million years. It also highlights the similarity between Mira AB and other jet-producing symbiotic binaries such as R Aquarii, CH Cygni, and MWC 560, and therefore raises the possibility that Mira B launched the recently discovered bipolar streams from this system.Comment: Accepted for publication in Ap