Magellan LDSS3 emission confirmation of galaxies hosting metal-rich Lyman-alpha absorption systems

Using the Low Dispersion Survey Spectrograph 3 at the Magellan II Clay Telescope, we target {candidate absorption host galaxies} detected in deep optical imaging {(reaching limiting apparent magnitudes of 23.0-26.5 in $g, r, i,$ and $z$ filters) in the fields of three QSOs, each of which shows the presence of high metallicity, high $N_{\rm HI}$ absorption systems in their spectra (Q0826-2230: $z_{abs}$=0.9110, Q1323-0021: $z_{abs}=0.7160$, Q1436-0051: $z_{abs}=0.7377, 0.9281$). We confirm three host galaxies {at redshifts 0.7387, 0.7401, and 0.9286} for two of the Lyman-$\alpha$ absorption systems (one with two galaxies interacting). For these systems, we are able to determine the star formation rates (SFRs); impact parameters (from previous imaging detections); the velocity shift between the absorption and emission redshifts; and, for one system, also the emission metallicity.} Based on previous photometry, we find these galaxies have L$>$L$^{\ast}$. The [O II] SFRs for these galaxies are in the range $11-25$ M$_{\odot}$ yr$^{-1}$ {(uncorrected for dust)}, while the impact parameters lie in the range $35-54$ kpc. {Despite the fact that we have confirmed galaxies at 50 kpc from the QSO, no gradient in metallicity is indicated between the absorption metallicity along the QSO line of sight and the emission line metallicity in the galaxies.} We confirm the anti-correlation between impact parameter and $N_{\rm HI}$ from the literature. We also report the emission redshift of five other galaxies: three at $z_{em}>z_{QSO}$, and two (L$<$L$^{\ast}$) at $z_{em}<z_{QSO}$ not corresponding to any known absorption systems.Comment: 14 pages, 7 figures, 4 tables, accepted to MNRA

HD 145263: Spectral Observations of Silica Debris Disk Formation via Extreme Space Weathering?

We report here time domain infrared spectroscopy and optical photometry of the HD145263 silica-rich circumstellar disk system taken from 2003 through 2014. We find an F4V host star surrounded by a stable, massive 1e22 - 1e23 kg (M_Moon to M_Mars) dust disk. No disk gas was detected, and the primary star was seen rotating with a rapid ~1.75 day period. After resolving a problem with previously reported observations, we find the silica, Mg-olivine, and Fe-pyroxene mineralogy of the dust disk to be stable throughout, and very unusual compared to the ferromagnesian silicates typically found in primordial and debris disks. By comparison with mid-infrared spectral features of primitive solar system dust, we explore the possibility that HD 145263's circumstellar dust mineralogy occurred with preferential destruction of Fe-bearing olivines, metal sulfides, and water ice in an initially comet-like mineral mix and their replacement by Fe-bearing pyroxenes, amorphous pyroxene, and silica. We reject models based on vaporizing optical stellar megaflares, aqueous alteration, or giant hypervelocity impacts as unable to produce the observed mineralogy. Scenarios involving unusually high Si abundances are at odds with the normal stellar absorption near-infrared feature strengths for Mg, Fe, and Si. Models involving intense space weathering of a thin surface patina via moderate (T < 1300 K) heating and energetic ion sputtering due to a stellar superflare from the F4V primary are consistent with the observations. The space weathered patina should be reddened, contain copious amounts of nanophase Fe, and should be transient on timescales of decades unless replenished.Comment: 41 Pages, 5 Figures, 5 Tables, Accepted for publication in the Astrophysical Journa

Variability of Optical Counterparts in the Chandra Galactic Bulge Survey

We present optical lightcurves of variable stars consistent with the positions of X-ray sources identified with the Chandra X-ray Observatory for the Chandra Galactic Bulge Survey. Using data from the Mosaic-II instrument on the Blanco 4m Telescope at CTIO, we gathered time-resolved photometric data on timescales from $\sim2$ hr to 8 days over the $\frac{3}{4}$ of the X-ray survey containing sources from the initial GBS catalog. Among the lightcurve morphologies we identify are flickering in interacting binaries, eclipsing sources, dwarf nova outbursts, ellipsoidal variations, long period variables, spotted stars, and flare stars. $87\%$ of X-ray sources have at least one potential optical counterpart. $24\%$ of these candidate counterparts are detectably variable; a much greater fraction than expected for randomly selected field stars, which suggests that most of these variables are real counterparts. We discuss individual sources of interest, provide variability information on candidate counterparts, and discuss the characteristics of the variable population.Comment: Accepted for publication in the Astrophysical Journal Supplement

The Relationship Between X-ray Luminosity and Duty Cycle for Dwarf Novae and their Specific Frequency in the Inner Galaxy

We measure the duty cycles for an existing sample of well observed, nearby dwarf novae using data from AAVSO, and present a quantitative empirical relation between the duty cycle of dwarf novae outbursts and the X-ray luminosity of the system in quiescence. We have found that $\log DC=0.63(\pm0.21)\times(\log L_{X}({\rm erg\,s^{-1}})-31.3)-0.95(\pm0.1)$, where DC stands for duty cycle. We note that there is intrinsic scatter in this relation greater than what is expected from purely statistical errors. Using the dwarf nova X-ray luminosity functions from \citet{Pretorius12} and \citet{Byckling10}, we compare this relation to the number of dwarf novae in the Galactic Bulge Survey which were identified through optical outbursts during an 8-day long monitoring campaign. We find a specific frequency of X-ray bright ($L_{X}>10^{31}\,{\rm erg\,s^{-1}}$) Cataclysmic Variables undergoing Dwarf Novae outbursts in the direction of the Galactic Bulge of $6.6\pm4.7\times10^{-5}\,M_{\odot}^{-1}$. Such a specific frequency would give a Solar neighborhood space density of long period CVs of $\rho=5.6\pm3.9\times10^{-6}\,$pc$^{-3}$. We advocate the use of specific frequency in future work, given that projects like LSST will detect DNe well outside the distance range over which $\rho\approx{\textrm const}$.Comment: 9 pagers, 4 figures Accepted for publication in MNRA

The Chandra Galactic Bulge Survey: optical catalogue and point-source counterparts to X-ray sources

As part of the Chandra Galactic Bulge Survey (GBS), we present a catalogue of optical sources in the GBS footprint. This consists of two regions centered at Galactic latitude b = 1.5 degrees above and below the Galactic Centre, spanning (l x b) = (6x1) degrees. The catalogue consists of 2 or more epochs of observations for each line of sight in r', i' and H{\alpha} filters. It is complete down to r' = 20.2 and i' = 19.2 mag; the mean 5{\sigma} depth is r' = 22.5 and i' = 21.1 mag. The mean root-mean-square residuals of the astrometric solutions is 0.04 arcsec. We cross-correlate this optical catalogue with the 1640 unique X-ray sources detected in Chandra observations of the GBS area, and find candidate optical counterparts to 1480 X-ray sources. We use a false alarm probability analysis to estimate the contamination by interlopers, and expect ~ 10 per cent of optical counterparts to be chance alignments. To determine the most likely counterpart for each X-ray source, we compute the likelihood ratio for all optical sources within the 4{\sigma} X-ray error circle. This analysis yields 1480 potential counterparts (~ 90 per cent of the sample). 584 counterparts have saturated photometry (r'<17, i'<16), indicating these objects are likely foreground sources and the real counterparts. 171 candidate counterparts are detected only in the i'-band. These sources are good qLMXB and CV candidates as they are X-ray bright and likely located in the Bulge.Comment: 18 pages, 18 figures. Published in MNRAS. 2016MNRAS.458.4530

Spectroscopic classification of X-ray sources in the Galactic Bulge Survey

We present the classification of 26 optical counterparts to X-ray sources discovered in the Galactic Bulge Survey. We use (time-resolved) photometric and spectroscopic observations to classify the X-ray sources based on their multi-wavelength properties. We find a variety of source classes, spanning different phases of stellar/binary evolution. We classify CX21 as a quiescent cataclysmic variable (CV) below the period gap, and CX118 as a high accretion rate (nova-like) CV. CXB12 displays excess UV emission, and could contain a compact object with a giant star companion, making it a candidate symbiotic binary or quiescent low mass X-ray binary (although other scenarios cannot be ruled out). CXB34 is a magnetic CV (polar) that shows photometric evidence for a change in accretion state. The magnetic classification is based on the detection of X-ray pulsations with a period of 81 $\pm$ 2 min. CXB42 is identified as a young stellar object, namely a weak-lined T Tauri star exhibiting (to date unexplained) UX Ori-like photometric variability. The optical spectrum of CXB43 contains two (resolved) unidentified double-peaked emission lines. No known scenario, such as an AGN or symbiotic binary, can easily explain its characteristics. We additionally classify 20 objects as likely active stars based on optical spectroscopy, their X-ray to optical flux ratios and photometric variability. In 4 cases we identify the sources as binary stars.Comment: Accepted for publication in MNRA

Constraining the nature of the accreting binary in CXOGBS J174623.5-310550

We report optical and infrared observations of the X-ray source CXOGBS J174623.5-310550. This Galactic object was identified as a potential quiescent low-mass X-ray binary accreting from an M-type donor on the basis of optical spectroscopy and the broad Halpha emission line. The analysis of X-shooter spectroscopy covering 3 consecutive nights supports an M2/3-type spectral classification. Neither radial velocity variations nor rotational broadening is detected in the photospheric lines. No periodic variability is found in I- and r'-band light curves. We derive r' = 20.8, I = 19.2 and Ks = 16.6 for the optical and infrared counterparts with the M-type star contributing 90% to the I-band light. We estimate its distance to be 1.3-1.8 kpc. The lack of radial velocity variations implies that the M-type star is not the donor star in the X-ray binary. This could be an interloper or the outer body in a hierarchical triple. We constrain the accreting binary to be a < 2.2 hr orbital period eclipsing cataclysmic variable or a low-mass X-ray binary lying in the foreground of the Galactic Bulge.Comment: (9 pages, 5 figures, accepted for publication in MNRAS

Determinants of Acceptance of Cervical Cancer Screening in Dar es Salaam, Tanzania.

To describe how demographic characteristics and knowledge of cervical cancer influence screening acceptance among women living in Dar es Salaam, Tanzania. Multistage cluster sampling was carried out in 45 randomly selected streets in Dar es Salaam. Women between the ages of 25-59 who lived in the sampled streets were invited to a cervical cancer screening; 804 women accepted and 313 rejected the invitation. Information on demographic characteristics and knowledge of cervical cancer were obtained through structured questionnaire interviews. Women aged 35-44 and women aged 45-59 had increased ORs of 3.52 and 7.09, respectively, for accepting screening. Increased accepting rates were also found among single women (OR 2.43) and among women who had attended primary or secondary school (ORs of 1.81 and 1.94). Women who had 0-2 children were also more prone to accept screening in comparison with women who had five or more children (OR 3.21). Finally, knowledge of cervical cancer and awareness of the existing screening program were also associated with increased acceptance rates (ORs of 5.90 and 4.20). There are identifiable subgroups where cervical cancer screening can be increased in Dar es Salaam. Special attention should be paid to women of low education and women of high parity. In addition, knowledge and awareness raising campaigns that goes hand in hand with culturally acceptable screening services will likely lead to an increased uptake of cervical cancer screening

Software systems for operation, control, and monitoring of the EBEX instrument

We present the hardware and software systems implementing autonomous operation, distributed real-time monitoring, and control for the EBEX instrument. EBEX is a NASA-funded balloon-borne microwave polarimeter designed for a 14 day Antarctic flight that circumnavigates the pole. To meet its science goals the EBEX instrument autonomously executes several tasks in parallel: it collects attitude data and maintains pointing control in order to adhere to an observing schedule; tunes and operates up to 1920 TES bolometers and 120 SQUID amplifiers controlled by as many as 30 embedded computers; coordinates and dispatches jobs across an onboard computer network to manage this detector readout system; logs over 3~GiB/hour of science and housekeeping data to an onboard disk storage array; responds to a variety of commands and exogenous events; and downlinks multiple heterogeneous data streams representing a selected subset of the total logged data. Most of the systems implementing these functions have been tested during a recent engineering flight of the payload, and have proven to meet the target requirements. The EBEX ground segment couples uplink and downlink hardware to a client-server software stack, enabling real-time monitoring and command responsibility to be distributed across the public internet or other standard computer networks. Using the emerging dirfile standard as a uniform intermediate data format, a variety of front end programs provide access to different components and views of the downlinked data products. This distributed architecture was demonstrated operating across multiple widely dispersed sites prior to and during the EBEX engineering flight.Comment: 11 pages, to appear in Proceedings of SPIE Astronomical Telescopes and Instrumentation 2010; adjusted metadata for arXiv submissio