Spectroscopic confirmation of UV-bright white dwarfs from the Sandage Two-Color Survey of the Galactic Plane

We present spectroscopic observations confirming the identification of hot white dwarfs among UV-bright sources from the Sandage Two-color Survey of the Galactic plane and listed in the Lanning (Lan) catalog of such sources. A subsample of 213 UV bright Lan sources have been identified as candidate white dwarfs based on the detection of a significant proper motion. Spectroscopic observations of 46 candidates with the KPNO 2.1m telescope confirm 30 sources to be hydrogen white dwarfs with subtypes in the DA1-DA6 range, and with one of the stars (Lan 161) having an unresolved M dwarf as a companion. Five more sources are confirmed to be helium white dwarfs, with subtypes from DB3 to DB6. One source (Lan 364) is identified as a DZ 3 white dwarf, with strong lines of calcium. Three more stars are found to have featureless spectra (to within detection limits), and are thus classified as DC white dwarfs. In addition, three sources are found to be hot subdwarfs: Lan 20 and Lan 480 are classified as sdOB, and Lan 432 is classified sdB. The remaining four objects are found to be field F star interlopers. Physical parameters of the DA and DB white dwarfs are derived from model fits.Comment: To appear in the Astronomical Journa

Oxygen, α\alpha-element and iron abundance distributions in the inner part of the Galactic thin disc. II

We have derived the abundances of 36 chemical elements in one Cepheid star, ASAS 181024--2049.6, located R$_{\rm G}= 2.53$ kpc from the Galactic center. This star falls within a region of the inner thin disc poorly sampled in Cepheids. Our spectral analysis shows that iron, magnesium, silicon, calcium and titanium LTE abundances in that star support the presence of a plateau-like abundance distribution in the thin disc within 5 kpc of the Galactic center, as previously suggested by \cite{Maret15}. If confirmed, the flattening of the abundance gradient within that region could be the result of a decrease in the star formation rate due to dynamic effects, possibly from the central Galactic bar.Comment: 5 pages, 3 figure

The Solar Neighborhood XXVII: Discovery of New Proper Motion Stars with mu > 0.18 "/yr in the Southern Sky with 16.5 > R_59F > 18.0

Here we present 1584 new southern proper motion systems with mu > 0.18 "/yr and 16.5 > R_59F > 18.0. This search complements the six previous SuperCOSMOS-RECONS (SCR) proper motion searches of the southern sky for stars within the same proper motion range, but with R_59F < 16.5. As in previous papers, we present distance estimates for these systems and find that three systems are estimated to be within 25 pc, including one, SCR 1546-5534, possibly within the RECONS 10 pc horizon at 6.7 pc, making it the second nearest discovery of the searches. We find 97 white dwarf candidates with distance estimates between 10 and 120 pc, as well as 557 cool subdwarf candidates. The subdwarfs found in this paper make up nearly half of the subdwarf systems reported from our SCR searches, and are significantly redder than those discovered thus far. The SCR searches have now found 155 red dwarfs estimated to be within 25 pc, including 10 within 10 pc. In addition, 143 white dwarf candidates and 1155 cool subdwarf candidates have been discovered. The 1584 systems reported here augment the sample of 4724 systems previously discovered in our SCR searches, and imply that additional systems fainter than R_59F = 18.0 are yet to be discovered.Comment: 11 pages of text, seven figure

Know Your Neighborhood: A Detailed Model Atmosphere Analysis of Nearby White Dwarfs

We present improved atmospheric parameters of nearby white dwarfs lying within 20 pc of the Sun. The aim of the current study is to obtain the best statistical model of the least-biased sample of the white dwarf population. A homogeneous analysis of the local population is performed combining detailed spectroscopic and photometric analyses based on improved model atmosphere calculations for various spectral types including DA, DB, DC, DQ, and DZ stars. The spectroscopic technique is applied to all stars in our sample for which optical spectra are available. Photometric energy distributions, when available, are also combined to trigonometric parallax measurements to derive effective temperatures, stellar radii, as well as atmospheric compositions. A revised catalog of white dwarfs in the solar neighborhood is presented. We provide, for the first time, a comprehensive analysis of the mass distribution and the chemical distribution of white dwarf stars in a volume-limited sample.Comment: 104 pages, 22 figures, 2 tables, accepted for publication in the Astrophysical Journal Supplemen

Epithelial Cell Invasion by Actinobacillus Actinomycetemcomitans Strains From Restriction Fragment-Length Polymorphism Groups Associated With Juvenile Periodontitis or Carrier Status

The epithelial cell invasiveness of Actinobacillus actinomycetemcomitans strains of different restriction fragment-length polymorphism (RFLP) groups associated with disease conversion and asymptomatic carrier status in localized juvenile periodontitis was examined. Twenty clinical isolates were studied for their ability to invade KB monolayers, using the quantitative gentamicin killing assay. Five isolates were found to be invasive; five were not invasive; and the other 10 did not invade better than an invasion negative control Haemophilus aphrophilus strain ATCC 19415. Using probe-specific DNA fingerprinting, 11 strains were assigned to RFLP group II (disease–associated); 4 to RFLP type XIII (carrier status-associated); and the others to groups III, IV, V and VII. Eight isolates, all RFLP group II, were leukotoxin producers as determined by PCR amplification of the lkt promoter region. No correlation was found between invasiveness and RFLP group. Leukotoxin production was more associated with noninvasive than invasive strains

The Benchmark Ultracool Subdwarf HD 114762B: A Test of Low-Metallicity Atmospheric and Evolutionary Models

We present a near-infrared spectroscopic study of HD 114762B, the latest-type metal-poor companion discovered to date and the only ultracool subdwarf with a known metallicity, inferred from the primary star to be [Fe/H] = -0.7. We obtained a medium-resolution Keck/OSIRIS J-band spectrum and a low-resolution IRTF/SpeX 0.8-2.4 um spectrum of HD 114762B. HD 114762B exhibits spectral features common to both late-type dwarfs and subdwarfs, and we assign it a spectral type of d/sdM9 +/- 1. We use a Monte Carlo technique to fit PHOENIX/GAIA synthetic spectra to the observations, accounting for the coarsely-gridded nature of the models. Fits to the entire OSIRIS J-band and to the metal-sensitive J-band atomic absorption features (Fe I, K I, and Al I lines) yield model parameters that are most consistent with the metallicity of the primary star and the high surface gravity expected of old late-type objects. The effective temperatures and radii inferred from the model atmosphere fitting broadly agree with those predicted by the evolutionary models of Chabrier & Baraffe, and the model color-absolute magnitude relations accurately predict the metallicity of HD 114762B. We conclude that current low-mass, mildly metal-poor atmospheric and evolutionary models are mutually consistent for spectral fits to medium-resolution J-band spectra of HD 114762B, but are inconsistent for fits to low-resolution near-infrared spectra of mild subdwarfs. Finally, we develop a technique for estimating distances to ultracool subdwarfs based on a single near-infrared spectrum. We show that this "spectroscopic parallax" method enables distance estimates accurate to < 10% of parallactic distances for ultracool subdwarfs near the hydrogen burning minimum mass. (abridged)Comment: Accepted by ApJ; 23 pages, 20 figure

The Solar Neighborhood XXV: Discovery of New Proper Motion Stars with 0.40 "/yr > mu > 0.18 "/yr between Declinations -47 degrees and 00 degrees

We present 2817 new southern proper motion systems with 0.40 "/yr > mu > 0.18 "/yr and declination between -47 degrees and 00 degrees. This is a continuation of the SuperCOSMOS-RECONS (SCR) proper motion searches of the southern sky. We use the same photometric relations as previous searches to provide distance estimates based on the assumption that the objects are single main sequence stars. We find 79 new red dwarf systems predicted to be within 25 pc, including a few new components of previously known systems. Two systems - SCR 1731-2452 at 9.5 pc and SCR 1746-3214 at 9.9 pc - are anticipated to be within 10 pc. We also find 23 new white dwarf candidates with distance estimates of 15-66 pc, as well as 360 new red subdwarf candidates. With this search, we complete the SCR sweep of the southern sky for stars with mu > 0.18 "/yr and R_59F < 16.5, resulting in a total of 5042 objects in 4724 previously unreported proper motion systems. Here we provide selected comprehensive lists from our SCR proper motion search to date, including 152 red dwarf systems estimated to be within 25 pc (nine within 10 pc), 46 white dwarfs (ten within 25 pc), and 598 subdwarf candidates. The results of this search suggest that there are more nearby systems to be found at fainter magnitudes and lower proper motion limits than those probed so far.Comment: 47 pages, 16 of text. 7 figure