Direct Detections of Young Stars in Nearby Elliptical Galaxies

Small amounts of star formation in elliptical galaxies are suggested by several results: surprisingly young ages from optical line indices, cooling X-ray gas, and mid-IR dust emission. Such star formation has previously been difficult to directly detect, but using UV Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) imaging, we have identified individual young stars and star clusters in four nearby ellipticals. This technique is orders of magnitude more sensitive than other methods, allowing detections of star formation to 10^(-5) Msun/yr. Ongoing star formation is detected in all galaxies, including three ellipticals that have previously exhibited potential signposts of star forming conditions (NGC 4636, NGC 4697, and NGC 4374), as well as the typical "red and dead" NGC 3379. The current star formation in our closest targets, where we are most complete, is between 1-8x10^(-5) Msun/yr. The star formation history was roughly constant from 0.5-1.5 Gyr (at 3-5x10^(-4) Msun/yr), but decreased by a factor of several in the past 0.3 Gyr. Most star clusters have a mass between 10^2 - 10^4 Msun. The specific star formation rates of ~10^(-16) yr^(-1) (at the present day) or ~10^(-14) yr^(-1) (when averaging over the past Gyr) imply that a fraction 10^(-8) of the stellar mass is younger than 100 Myr and 10^(-5) is younger than 1 Gyr, quantifying the level of frosting of recent star formation over the otherwise passive stellar population. There is no obvious correlation between either the presence or spatial distribution of postulated star formation indicators and the star formation we detect.Comment: Accepted for publication in ApJ. 14 pages, 11 figure

Development of a noise annoyance sensitivity scale

Examining the problem of noise pollution from the psychological rather than the engineering view, a test of human sensitivity to noise was developed against the criterion of noise annoyance. Test development evolved from a previous study in which biographical, attitudinal, and personality data was collected on a sample of 166 subjects drawn from the adult community of Raleigh. Analysis revealed that only a small subset of the data collected was predictive of noise annoyance. Item analysis yielded 74 predictive items that composed the preliminary noise sensitivity test. This was administered to a sample of 80 adults who later rate the annoyance value of six sounds (equated in terms of peak sound pressure level) presented in a simulated home, living-room environment. A predictive model involving 20 test items was developed using multiple regression techniques, and an item weighting scheme was evaluated

The Search for Million Degree Gas Through The NVII Hyperfine Line

Gas in the million degree range occurs in a variety of astronomical environments, and it may be the main component of the elusive missing baryons at low redshift. The NVII ion is found in this material and it has a hyperfine spin-flip transition with a rest frequency of 53.042 GHz, which can be observed for z > 0.1, when it is shifted into a suitably transparent radio band. We used the 42-48 GHz spectrometer on the Green Bank Telescope to search for both emission and absorption from this NVII transmission. For absorption studies, 3C273, 3C 279, 3C 345, and 4C+39.25 were observed but no feature were seen above the 5 sigma level. For emission line studies, we observed Abell 1835, Abell 2390 and the star-forming galaxy PKS 1345+12, but no features were seen exceeding 5 sigma. We examine whether the strongest emission feature, in Abell 2390 (3.7 sigma), and the strongest absorption feature, toward 4C+39.25 (3.8 sigma), might be expected from theoretical models. The emission feature would require ~1E10 Msolar of 1E6 K gas, which is inconsistent with X-ray limits for the O VII Kalpha line, so it is unlikely to be real. The NVII absorption feature requires a NVII column of 6E16 cm^-2, higher than model predictions by at least an order of magnitude, which makes it inconsistent with model expectations. The individual observations were less than 1 hr in length, so for lengthy observations, we show that NVII absorption line observations can begin to be useful in in the search for hot intergalactic gas.Comment: 27 total pages; 16 figures; Accepted for publication in The Astrophysical Journa

Low-background performance of a monolithic InSb CCD array

A 20 element monolithic InSb charge coupled device (CCD) detector array was measured under low background conditions to assess its potential for orbital astronomical applications. At a temperature of 64 K, previous results for charge transfer efficiency (CTE) were reproduced, and a sensitivity of about 2 x 10 to the minus 15th power joules was measured. At 27 and 6 K, extended integration times were achieved, but CTE was substantially degraded. The noise was approximately 6000 charges, which was in excess of the level where statistical fluctuations from the illumination could be detected. A telescope demonstration was performed showing that the array sensitivity and difficulty of operation were not substantially different from laboratory levels. Ways in which the device could be improved for astronomical applications were discussed

A modified band approach for the accurate calculation of online photolysis rates in stratospheric-tropospheric Chemical Transport Models

International audienceHere we present an efficient and accurate method for the online calculation of photolysis rates relevant to both the stratosphere and troposphere for use in global Chemistry Transport Models and General Circulation Models. The method is a modified version of the band model introduced by Landgraf and Crutzen (1998) which has been updated to improve the performance of the approach for solar zenith angles >72° without the use of any implicit parameterisations. For this purpose, additional sets of band parameters have been defined for instances where the incident angle of the light beam is between 72?93°, in conjunction with a scaling component for the far UV region of the spectrum (?=178.6?202.0 nm). For incident angles between 85?93° we introduce a modification for pseudo-sphericity that improves the accuracy of the 2-stream approximation. We show that this modified version of the Practical Improved Flux Method (PIFM) is accurate for angles <93° by comparing the resulting height resolved actinic fluxes with a recently developed full spherical reference model. We also show that the modified band method is more accurate than the original, with errors generally being less than ±10% throughout the atmospheric column for a diverse range of chemical species. Moreover, we perform certain sensitivity studies that indicate it is robust and performs well over a wide range of conditions relevant to the atmosphere

The Effect of Environment on the X-Ray Emission from Early-Type Galaxies

In order to help understand the phenomena of X-ray emission from early-type galaxies, we obtained an optically flux-limited sample of 34 early-type galaxies, observed with ROSAT. A previous analysis of this sample suggested that the most X-ray luminous galaxies were in rich environments. Here we investigate environmental influences quantitatively, and find a positive correlation between L_B/L_X and the local galaxy density. We suggest that this correlation occurs because the X-ray luminosity is enhanced either through accretion of the intergalactic gas or because the ambient medium stifles galactic winds. When the ambient medium is unimportant, partial or global galactic winds can occur, reducing L_B/L_X. These effects lead to the large observed dispersion in L_X at fixed L_B. We argue that the transition from global winds to partial winds is one of the principle reasons for the steep relationship between L_X and L_B. We discuss details of the data reduction not previously presented, and examine the dependence of L_X on the choice of outer source radius and background location. Effects of Malmquist bias are shown not to be important for the issues addressed. Finally, we compare the temperature deduced for these galaxies from different analyses of ROSAT and ASCA data.Comment: 29 pages, including 6 figures (ps); AASTeX 12pt,aaspp4 format; submitted to Ap

Fast Primal-Dual Gradient Method for Strongly Convex Minimization Problems with Linear Constraints

In this paper we consider a class of optimization problems with a strongly convex objective function and the feasible set given by an intersection of a simple convex set with a set given by a number of linear equality and inequality constraints. A number of optimization problems in applications can be stated in this form, examples being the entropy-linear programming, the ridge regression, the elastic net, the regularized optimal transport, etc. We extend the Fast Gradient Method applied to the dual problem in order to make it primal-dual so that it allows not only to solve the dual problem, but also to construct nearly optimal and nearly feasible solution of the primal problem. We also prove a theorem about the convergence rate for the proposed algorithm in terms of the objective function and the linear constraints infeasibility.Comment: Submitted for DOOR 201

Confirming the Detection of an Intergalactic X-ray Absorber Toward PKS 2155-304

We present new observations on PKS 2155-304 with the Chandra Low Energy Transmission Grating Spectrometer (LETG), using the Advanced CCD Imaging Spectrometer (ACIS). We confirm the detection of an absorption line plausibly identified as OVIII Ly-alpha from the warm-hot intergalactic medium associated with a small group of galaxies along the line of sight, as originally reported by Fang et al. 2002 (here after FANG02). Combining the previous observations in FANG02 and five new, long observations on the same target, we increase the total exposure time by a factor of three, and the total counts per resolution element by a factor of five. The measured line equivalent width is smaller than that observed in FANG02, but still consistent at 90% confidence. We also analyze the XMM-Newton observations on the same target, as well as observations using the Chandra LETG and the High Resolution Camera (HRC) combination. These observations have been used to challenge our reported detection. While no line is seen in either the XMM-Newton and the Chandra LETG+HRC data, we find that our result is consistent with the upper limits from both data sets. We attribute the non-detection to (1) higher quality of the Chandra LETG+ACIS spectrum, and (2) the rather extended wings of the line spread functions of both the XMM RGS and the Chandra LETG+HRC. We discuss the implication of our observation on the temperature and density of the absorber. We also confirm the detection of z ~ 0 OVII absorption and, comparing with previous Chandra analysis, we obtain much tighter constraints on the line properties.Comment: 10 pages, 8 figures, accepted for publication in Ap

Infrared spectra of WC10 planetary nebulae nuclei

The 5.2 to 8.0 micron spectra are presented for two planetary nebulae nuclei Hen1044 (He2-113) and CPD-56 8032. The unidentified infrared (UIR) emission bands at 6.2 microns, 6.9 microns, 7.7 microns are present in the spectra of Hen1044 and in CPD-56 8032, and the 8.6 micron band is present in the long wavelength shoulder of the 7.7 micron band in the spectrum of CPD-56 8032. The 8 to 13 micron spectra of these two stars by Aitken et. al. clearly show the presence of the 8.6 micron band in He2-113 while weakly resolving this feature in the spectra of CPD-56 8032. In their spectra the 11.3 micron band is also clearly detected in both objects. The 6.2 micron and 7.7 micron bands are characteristic of the infrared active C-C stretching modes in polycyclic aromatic hydrocarbons (PAHs); the 3.3 micron, 8.6 micron, and 11.3 micron bands are respectively assigned to the in-plane stretching mode, the in-plane bending mode, and the out-of-plane bending mode of the aromatic CH bond. The weak 6.9 micron emission feature is attributed to the UIR spectrum by Bregman et. al. The IRAS LRS spectra of He2-113 (IRAS 14562-5406) and CPD-56 8032 (IRAS 17047-5650) are presented. Cohen et. al. identify the broad plateau from 11.3 to 13.0 microns in the spectrum of He2-113 with increased hydrogenation of PAHs. This broad plateau is not seen in the LRS spectrum of CPD-56 8032. Also, He2-113 has greater infrared excess emission in the 17-22 micron region than does CPD-56 8032

Radiation survival of murine and human melanoma cells utilizing two assay systems: monolayer and soft agar.

The radiation response of murine and human melanoma cells assayed in bilayer soft agar and monolayer was examined. Cells from the murine melanoma Cloudman S91 CCL 53.1 cell line and three human melanoma cell strains (C8146C, C8161, and R83-4) developed in our laboratory were irradiated by single dose X-rays and plated either in agar or on plastic. D0 values were the same within 95% confidence intervals for cells from the human melanoma cell strains C8146C, C8161, and R83-4 but were dissimilar for the murine cell line CCL 53.1 Dq values were different for all cells studied. The shape of the survival curve for all four melanomas was not identical for cells assayed in soft agar versus cells grown on plastic. This would indicate that apparent radiosensitivity was influenced by the method of assay although there were no apparent consistent differences between the curves generated by monolayer or bilayer soft agar assays