706 research outputs found
Ceramic coating effect on liner metal temperatures of film-cooled annular combustor
An experimental and analytical investigation was conducted to determine the effect of a ceramic coating on the average metal temperatures of full annular, film cooled combustion chamber liner. The investigation was conducted at pressures from 0.50 to 0.062. At all test conditions, experimental results indicate that application of a ceramic coating will result in significantly lower wall temperatures. In a simplified heat transfer analysis, agreement between experimental and calculated liner temperatures was achieved. Simulated spalling of a small portion of the ceramic coating resulted in only small increases in liner temperature because of the thermal conduction of heat from the hotter, uncoated liner metal
Turbine blade metal temperature measurement with a sputtered thin film chromel-alumel thermocouple
A technique for fabricating Chromel and Alumel thin film thermocouples was developed. Turbine blade metal temperatures measured with the thin film thermocouple installation were compared with those of a reference sheathed (wire) thermocouple. Good agreement was obtained, and the results are encouraging
Discovery of a Magnetic DZ White Dwarf with Zeeman-Split Lines of Heavy Elements
A spectroscopic survey of previously-unstudied Luyten Half Second proper
motion stars has resulted in the discoveries of two new cool magnetic white
dwarfs. One (LHS 2273) is a routine DA star, T= 6,500K, with Zeeman-split H
alpha and H beta, for which a simple model suggests a polar field strength of
18.5 MG viewed close to equator-on. However, the white dwarf LHS 2534 proves to
be the first magnetic DZ showing Zeeman-split Na I and Mg I components, as well
as Ca I and Ca II lines for which Zeeman components are blended. The Na I
splittings result in a mean surface field strength estimate of 1.92 MG. Apart
from the magnetic field, LHS 2534 is one of the most heavily-blanketed and
coolest DZ white dwarfs at T ~ 6,000K.Comment: 7 pages, Astrophysical Journal (Letters), in pres
The Ages of the Thin Disk, Thick Disk, and the Halo from Nearby White Dwarfs
We present a detailed analysis of the white dwarf luminosity functions
derived from the local 40 pc sample and the deep proper motion catalog of Munn
et al (2014, 2017). Many of the previous studies ignored the contribution of
thick disk white dwarfs to the Galactic disk luminosity function, which results
in an erronous age measurement. We demonstrate that the ratio of thick/thin
disk white dwarfs is roughly 20\% in the local sample. Simultaneously fitting
for both disk components, we derive ages of 6.8-7.0 Gyr for the thin disk and
8.7 0.1 Gyr for the thick disk from the local 40 pc sample. Similarly, we
derive ages of 7.4-8.2 Gyr for the thin disk and 9.5-9.9 Gyr for the thick disk
from the deep proper motion catalog, which shows no evidence of a deviation
from a constant star formation rate in the past 2.5 Gyr. We constrain the time
difference between the onset of star formation in the thin disk and the thick
disk to be Gyr. The faint end of the luminosity function
for the halo white dwarfs is less constrained, resulting in an age estimate of
Gyr for the Galactic inner halo. This is the first time
ages for all three major components of the Galaxy are obtained from a sample of
field white dwarfs that is large enough to contain significant numbers of disk
and halo objects. The resultant ages agree reasonably well with the age
estimates for the oldest open and globular clusters.Comment: ApJ, in pres
Mutated Measles Virus Matrix and Fusion Protein Influence Viral Titer In Vitro and Neuro-Invasion in Lewis Rat Brain Slice Cultures
Measles virus (MV) can cause severe acute diseases as well as long-lasting clinical deteriorations due to viral-induced immunosuppression and neuronal manifestation. How the virus enters the brain and manages to persist in neuronal tissue is not fully understood. Various mutations in the viral genes were found in MV strains isolated from patient brains. In this study, reverse genetics was used to introduce mutations in the fusion, matrix and polymerase genes of MV. The generated virus clones were characterized in cell culture and used to infect rat brain slice cultures. A mutation in the carboxy-terminal domain of the matrix protein (R293Q) promoted the production of progeny virions. This effect was observed in Vero cells irrespective of the expression of the signaling lymphocyte activation molecule (SLAM). Furthermore, a mutation in the fusion protein (I225M) induced syncytia formation on Vero cells in the absence of SLAM and promoted viral spread throughout the rat brain slices. In this study, a solid ex vivo model was established to elucidate the MV mutations contributing to neural manifestation
No Neutron Star Companion To The Lowest Mass SDSS White Dwarf
SDSS J091709.55+463821.8 (hereafter J0917+4638) is the lowest surface gravity
white dwarf (WD) currently known, with log g = 5.55 +/- 0.05 (M ~ 0.17 M_sun;
Kilic et al. 2007a,b). Such low-mass white dwarfs (LMWDs) are believed to
originate in binaries that evolve into WD/WD or WD/neutron star (NS) systems.
An optical search for J0917+4638's companion showed that it must be a compact
object with a mass >= 0.28 M_sun (Kilic 2007b). Here we report on Green Bank
Telescope 820 MHz and XMM-Newton X-ray observations of J0917+4638 intended to
uncover a potential NS companion to the LMWD. No convincing pulsar signal is
detected in our radio data. Our X-ray observation also failed to detect X-ray
emission from J0917+4638's companion, while we would have detected any of the
millisecond radio pulsars in 47 Tuc. We conclude that the companion is almost
certainly another WD.Comment: 4 pages, 1 table; to appear in the Astrophysical Journal Letter
Multiwavelength Observations of the Hot DB Star PG 0112+104
We present a comprehensive multiwavelength analysis of the hot DB white dwarf
PG 0112+104. Our analysis relies on newly-acquired FUSE observations, on
medium-resolution FOS and GHRS data, on archival high-resolution GHRS
observations, on optical spectrophotometry both in the blue and around Halpha,
as well as on time-resolved photometry. From the optical data, we derive a
self-consistent effective temperature of 31,300+-500 K, a surface gravity of
log g = 7.8 +- 0.1 (M=0.52 Msun), and a hydrogen abundance of log N(H)/N(He) <
-4.0. The FUSE spectra reveal the presence of CII and CIII lines that
complement the previous detection of CII transitions with the GHRS. The
improved carbon abundance in this hot object is log N(C)/N(He) = -6.15 +- 0.23.
No photospheric features associated with other heavy elements are detected. We
reconsider the role of PG 0112+104 in the definition of the blue edge of the
V777 Her instability strip in light of our high-speed photometry, and contrast
our results with those of previous observations carried out at the McDonald
Observatory.Comment: 10 pages in emulateapj, 9 figures, accepted for publication in Ap
First Results from Pan-STARRS1: Faint, High Proper Motion White Dwarfs in the Medium-Deep Fields
The Pan-STARRS1 survey has obtained multi-epoch imaging in five bands
(Pan-STARRS1 gps, rps, ips, zps, and yps) on twelve "Medium Deep Fields", each
of which spans a 3.3 degree circle. For the period between Apr 2009 and Apr
2011 these fields were observed 50-200 times. Using a reduced proper motion
diagram, we have extracted a list of 47 white dwarf (WD) candidates whose
Pan-STARRS1 astrometry indicates a non-zero proper motion at the 6-sigma level,
with a typical 1-sigma proper motion uncertainty of 10 mas/yr. We also used
astrometry from SDSS (when available) and USNO-B to assess our proper motion
fits. None of the WD candidates exhibits evidence of statistically significant
parallaxes, with a typical 1-sigma uncertainty of 8 mas. Twelve of these
candidates are known WDs, including the high proper motion (1.7"/yr) WD LHS
291. We confirm three more objects as WDs through optical spectroscopy. Based
on the Pan-STARRS1 colors, ten of the stars are likely to be cool WDs with 4170
K Teff 5000 K and cooling ages <9 Gyr. We classify these objects as likely
thick disk WDs based on their kinematics. Our current sample represents only a
small fraction of the Pan-STARRS1 data. With continued coverage from the Medium
Deep Field Survey and the 3pi survey, Pan-STARRS1 should find many more high
proper motion WDs that are part of the old thick disk and halo.Comment: 33 pages, 8 figures, submitted to Ap
Simultaneous Multi-Wavelength Observations of Magnetic Activity in Ultracool Dwarfs. I. The Complex Behavior of the M8.5 Dwarf TVLM513-46546
[Abridged] We present the first simultaneous radio, X-ray, ultraviolet, and
optical spectroscopic observations of the M8.5 dwarf TVLM513-46546, with a
duration of 9 hours. These observations are part of a program to study the
origin of magnetic activity in ultracool dwarfs, and its impact on
chromospheric and coronal emission. Here we detect steady quiescent radio
emission superposed with multiple short-duration, highly polarized flares;
there is no evidence for periodic bursts previously reported for this object,
indicating their transient nature. We also detect soft X-ray emission, with
L_X/L_bol~10^-4.9, the faintest to date for any object later than M5, and a
possible weak X-ray flare. TVLM513-46546 continues the trend of severe
violation of the radio/X-ray correlation in ultracool dwarfs, by nearly 4
orders of magnitude. From the optical spectroscopy we find that the Balmer line
luminosity exceeds the X-ray luminosity by a factor of a few, suggesting that,
unlike in early M dwarfs, chromospheric heating may not be due to coronal X-ray
emission. More importantly, we detect a sinusoidal H-alpha light curve with a
period of 2 hr, matching the rotation period of TVLM513-46546. This is the
first known example of such Balmer line behavior, which points to a co-rotating
chromospheric hot spot or an extended magnetic structure, with a covering
fraction of about 50%. This feature may be transitory based on the apparent
decline in light curve peak during the four observed maxima. From the radio
data we infer a large scale steady magnetic field of ~100 G, in good agreement
with the value required for confinement of the X-ray emitting plasma. The radio
flares, on the other hand, are produced in a component of the field with a
strength of ~3 kG and a likely multi-polar configuration.Comment: 13 pages, 4 figure
Blue Horizontal Branch Stars in Old, Metal-Rich Stellar Systems
Twenty years ago, Burstein et al. (1984)suggested that strong CN and Hbeta absorption meant younger ages among globular clusters in the Andromeda galaxy (M31), unless blue stars above the main-sequence turnoff or on the horizontal branch were uncommonly prominent. Here we test these suggestions by fitting the detailed mid-ultraviolet (2280-3120A) and optical (3850-4750A) spectra of one moderately metal-rich M31 globular cluster, G1. We explore the effects of a wide range of non-solar temperatures and abundance ratios, by combining a small set of theoretical stellar spectra like those of Peterson et al. (2001) that were calculated using extensively updated atomic-line constants. To match the mid-UV fluxes of G1, we find that hot components with Teff >= 8000K must be included. We obtain a very good fit with cool and hot blue horizontal branch (BHB) stars, but less satisfactory fits for blue straggler stars, those hotter than the main-sequence turnoff. The G1 color-magnitude diagram does show cool BHB stars, and the color of its giant branch supports the metallicity of one-sixth the solar value that we deduce. The turnoff temperature of the best-fit model is consistent with that of turnoff stars in galactic globular clusters and the field halo, indicating G1 is comparably old. Because metal-rich cool BHB and extremely blue HB stars have now been found within our own Galaxy, we suggest that these hot horizontal-branch stars be considered in fitting spectra of metal-rich populations such as the Andromeda globular clusters, to avoid possible underestimates of their ages. We plan to make the relevant spectral calculations available as part of our Hubble Treasury Program
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