584 research outputs found
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
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
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
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
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
Discovery of a 0.15" Binary Brown Dwarf 2MASSJ 1426316+155701 With Gemini/Hokupa'a Adaptive Optics
Use of the highly sensitive Hokupa'a curvature wavefront sensor has allowed
for the first time direct adaptive optics (AO) guiding on brown dwarfs and VLM
stars (SpT=M7-L2). An initial survey of 9 such objects discovered one 0.15"
binary (2MASSJ 1426316+155701). The companion is about half as bright as the
primary (Delta K = 0.61+/-0.05. These spectral types also match the
observed H-K colors of each star. Based the previously observed low space
motion and activity we assign an age of .
Utilizing this age range and the latest DUSTY models of the Lyon group we
assign a photometric distance of and masses of
and . We therefore estimate a system separation of
and a period of respectively. Hence, 2M1426 is among
the smallest separation brown dwarf binaries resolved to date
Geometrical Aberration Suppression for Large Aperture Sub-THz Lenses
Advanced THz setups require high performance optical elements with large numerical apertures and small focal lengths. This is due to the high absorption of humid air and relatively low efficiency of commercially available detectors. Here, we propose a new type of double-sided sub-THz diffractive optical element with suppressed geometrical aberration for narrowband applications (0.3 THz). One side of the element is designed as thin structure in non-paraxial approach which is the exact method, but only for ideally flat elements. The second side will compensate phase distribution differences between ideal thin structure and real volume one. The computer-aided optimization algorithm is performed to design an additional phase distribution of correcting layer assuming volume designing of the first side of the element. The experimental evaluation of the proposed diffractive component created by 3D printing technique shows almost two times larger performance in comparison with uncorrected basic diffractive lens
Spectroscopic Identification of Faint White Dwarf Candidates in the Praesepe Open Star Cluster
We present spectroscopic observations of the remaining four candidate white
dwarfs in Praesepe. All four candidates are quasars with redshifts between 0.8
and 2.8. One quasar, LB 6072, is observed to have a strong metal-line
absorption system blueward of the quasar redshift. The lack of additional white
dwarfs in Praesepe leaves the total known white-dwarf population of the cluster
at five, well below the number expected from commonly-assumed initial mass
functions, though several undiscovered cluster WDs may lie in the outer regions
of the cluster. All known Praesepe member white dwarfs are concentrated within
0.6 deg of the cluster center, and the radial profile of cluster white dwarfs
is quite similar to the profile of massive cluster stars. This profile is
mildly inconsistent with that of ~1Mo cluster stars and suggests that the white
dwarfs did not receive a velocity kick during the progenitor star's mass loss
phases. If complete, the observed Praesepe white dwarf population is consistent
with a steeper high-end initial-mass function than commonly assumed, though the
calculated slopes are inconsistent with the present-day mass function of
Praesepe. Searches for white dwarfs outside the core of Praesepe and further
study of the white dwarf populations of additional open clusters is necessary
to constrain further the underlying cause of the white dwarf deficit.Comment: 6 pages, 5 figures, uses emulateapj.cls; accepted for publication in
the Astronomical Journa
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