3,625 research outputs found
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Crowdsourcing in the Quaternary sea level community: insights from the Pliocene
In order to establish the âfingerprintâ of past sea level changes, many field measurements of paleo sea level from globally distributed locations are needed. It is because this problem requires a geographically expansive database that it becomes an ideal candidate for crowdsourcing techniques. In order to crowdsource sea level data from the Mid-Pliocene Warm Period, we developed three tools: PlioWiki, RSLcalc and RSLmap. PlioWiki is a web portal, open to contributions, where investigators can share knowledge on Pliocene to Quaternary relative sea levels. RSLcalc is a standardized, ready-to-use tool for field geologists to log their own sea level field observations and, if they desire, submit new data to an open access database of relative sea level markers. RSLmap allows one to visualize and query the database built with RSLcalc on a Google Map interface. Here we describe these tools and discuss the advantages of crowdsourcing, relative to traditional approaches, for the creation of sea level databases for any time period
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The Mid-Pliocene sea-level conundrum: Glacial isostasy, eustasy and dynamic topography
Determining eustatic sea level during the Mid-Pliocene warm period (~ 3.3 to 2.9 Ma) has been a central but elusive goal in the study of past warm climates. Estimates of eustatic sea level based on geologic data span a broad range; variation that we now recognize is due in part to geographically varying post-depositional displacement caused by glacial isostatic adjustment and dynamic topography. In this study, we combine field observations and glacial isostatic adjustment modeling to estimate the dynamic topography signal in three areas that are important to paleo-sea level studies of the Mid-Pliocene warm period (South Africa, West Australia and southeastern United States). We show that dynamic topography played a significant role in the post-depositional displacement of Pliocene, and even younger Pleistocene, shorelines. In this regard, we provide a robust paleo-sea level elevation data set, corrected for glacial isostatic adjustment, that can be used to evaluate predictions from mantle flow models of dynamic topography
Overview of the spectrometer optical fiber feed for the Habitable-zone Planet Finder
The Habitable-zone Planet Finder (HPF) is a highly stabilized fiber fed
precision radial velocity (RV) spectrograph working in the Near Infrared (NIR):
810 - 1280 nm . In this paper we present an overview of the preparation of the
optical fibers for HPF. The entire fiber train from the telescope focus down to
the cryostat is detailed. We also discuss the fiber polishing, splicing and its
integration into the instrument using a fused silica puck. HPF was designed to
be able to operate in two modes, High Resolution (HR- the only mode mode
currently commissioned) and High Efficiency (HE). We discuss these fiber heads
and the procedure we adopted to attach the slit on to the HR fibers.Comment: Presented at 2018 SPIE Astronomical Telescopes + Instrumentation,
Austin, Texas, USA. 18 pages, 25 figures, and 2 table
AzTEC 1.1 mm Observations of the MBM12 Molecular Cloud
We present 1.1 mm observations of the dust continuum emission from the MBM12
high-latitude molecular cloud observed with the Astronomical Thermal Emission
Camera (AzTEC) mounted on the James Clerk Maxwell Telescope on Mauna Kea,
Hawaii. We surveyed a 6.34 deg centered on MBM12, making this the largest
area that has ever been surveyed in this region with submillimeter and
millimeter telescopes. Eight secure individual sources were detected with a
signal-to-noise ratio of over 4.4. These eight AzTEC sources can be considered
to be real astronomical objects compared to the other candidates based on
calculations of the false detection rate. The distribution of the detected 1.1
mm sources or compact 1.1 mm peaks is spatially anti-correlated with that of
the 100 micronm emission and the CO emission. We detected the 1.1 mm
dust continuum emitting sources associated with two classical T Tauri stars,
LkHalpha262 and LkHalpha264. Observations of spectral energy distributions
(SEDs) indicate that LkHalpha262 is likely to be Class II (pre-main-sequence
star), but there are also indications that it could be a late Class I
(protostar). A flared disk and a bipolar cavity in the models of Class I
sources lead to more complicated SEDs. From the present AzTEC observations of
the MBM12 region, it appears that other sources detected with AzTEC are likely
to be extragalactic and located behind MBM12. Some of these have radio
counterparts and their star formation rates are derived from a fit of the SEDs
to the photometric evolution of galaxies in which the effects of a dusty
interstellar medium have been included.Comment: 8 pages, 6 figures, The Astrophysical Journal, in pres
A Prediction of Brown Dwarfs in Ultracold Molecular Gas
A recent model for the stellar initial mass function (IMF), in which the
stellar masses are randomly sampled down to the thermal Jeans mass from
hierarchically structured pre-stellar clouds, predicts that regions of
ultra-cold CO gas, such as those recently found in nearby galaxies by Allen and
collaborators, should make an abundance of Brown Dwarfs with relatively few
normal stars. This result comes from the low value of the thermal Jeans mass,
considering that the hierarchical cloud model always gives the Salpeter IMF
slope above this lower mass limit. The ultracold CO clouds in the inner disk of
M31 have T~3K and pressures that are probably 10 times higher than in the solar
neighborhood. This gives a mass at the peak of the IMF equal to 0.01 Msun, well
below the Brown Dwarf limit of 0.08 Msun. Using a functional approximation to
the IMF, the ultracold clouds would have 50% of the star-like mass and 90% of
the objects below the Brown Dwarf limit. The brightest of the Brown Dwarfs in
M31 should have an apparent, extinction-corrected K-band magnitude of ~21 mag
in their pre-main sequence phase.Comment: 13 pages, 2 figures, to be published in Astrophysical Journal, Vol
522, September 10, 199
Extinction Maps Toward The Milky Way Bulge: Two-Dimensional And Three-Dimensional Tests With APOGEE
Galactic interstellar extinction maps are powerful and necessary tools for Milky Way structure and stellar population analyses, particularly toward the heavily reddened bulge and in the midplane. However, due to the difficulty of obtaining reliable extinction measures and distances for a large number of stars that are independent of these maps, tests of their accuracy and systematics have been limited. Our goal is to assess a variety of photometric stellar extinction estimates, including both two-dimensional and three-dimensional extinction maps, using independent extinction measures based on a large spectroscopic sample of stars toward the Milky Way bulge. We employ stellar atmospheric parameters derived from high-resolution H-band Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectra, combined with theoretical stellar isochrones, to calculate line-of-sight extinction and distances for a sample of more than 2400 giants toward the Milky Way bulge. We compare these extinction values to those predicted by individual near-IR and near+mid-IR stellar colors, two-dimensional bulge extinction maps, and three-dimensional extinction maps. The long baseline, near+mid-IR stellar colors are, on average, the most accurate predictors of the APOGEE extinction estimates, and the two-dimensional and three-dimensional extinction maps derived from different stellar populations along different sightlines show varying degrees of reliability. We present the results of all of the comparisons and discuss reasons for the observed discrepancies. We also demonstrate how the particular stellar atmospheric models adopted can have a strong impact on this type of analysis, and discuss related caveats.NSF Astronomy & Astrophysics Postdoctoral Fellowship AST-1203017Physics Frontier Center/Joint Institute for Nuclear Astrophysics (JINA) PHY 08-22648U.S. National Science FoundationAlfred P. Sloan FoundationParticipating InstitutionsU.S. Department of Energy Office of Science ANR-12-BS05-0015-01Astronom
System Performance Comparison of R-407A and R-502 in Parallel and Counter-Flow Heat Exchangers
Low Mass Stars and Substellar Objects in the NGC 1333 Molecular Cloud
We present the results of near-infrared imaging and low-resolution near-
infrared spectroscopy of low mass objects in the NGC 1333 molecular cloud. A
JHK survey of an 11.4' x 11.7' area of the northern cluster was conducted to a
sensitivity of K < 16 mag. Using near-infrared magnitudes and colors from this
and previously published surveys, twenty-five brown dwarf candidates were
selected toward the high extinction cloud core. Spectra in the K band were
obtained and comparisons of the depths of water vapor absorption bands in our
candidate objects with a grid of dwarf,subgiant, and giant standards were made
to derive spectral types. These data were then used to derive effective
temperatures and stellar luminosities which, when combined with theoretical
tracks and isochrones for pre-main sequence objects, resulted in estimates for
their masses and ages. The models suggest a median age for the sample of < 1
Myr with substellar masses for at least 9 of the candidates including the x-ray
flare source ASR 24. Surface gravities have been estimated for the brown dwarf
candidates and, for a given spectral type,found to resemble more closely dwarfs
than giants. Using the near-infrared imaging data and age estimates from the
spectroscopic sample, an extinction-limited sample in the northern cluster was
defined. Consistent with recent studies of other young clusters, this sample
exhibits an accretion disk frequency of 0.75 +-0.20 and a mass spectrum slope
across the hydrogen-burning limit of alpha < 1.6 where dN/dM ~ M^-(alpha).Comment: 22 postscript pages, 12 postscript figures, and 3 postscript tables.
Accepted for publication in the Astronomical Journal (February, 2004
The SDSS-III APOGEE Radial Velocity Survey of M dwarfs I: Description of Survey and Science Goals
We are carrying out a large ancillary program with the SDSS-III, using the
fiber-fed multi-object NIR APOGEE spectrograph, to obtain high-resolution
H-band spectra of more than 1200 M dwarfs. These observations are used to
measure spectroscopic rotational velocities, radial velocities, physical
stellar parameters, and variability of the target stars. Here, we describe the
target selection for this survey and results from the first year of scientific
observations based on spectra that is publicly available in the SDSS-III DR10
data release. As part of this paper we present RVs and vsini of over 200 M
dwarfs, with a vsini precision of ~2 km/s and a measurement floor at vsini = 4
km/s. This survey significantly increases the number of M dwarfs studied for
vsini and RV variability (at ~100-200 m/s), and will advance the target
selection for planned RV and photometric searches for low mass exoplanets
around M dwarfs, such as HPF, CARMENES, and TESS. Multiple epochs of radial
velocity observations enable us to identify short period binaries, and AO
imaging of a subset of stars enables the detection of possible stellar
companions at larger separations. The high-resolution H-band APOGEE spectra
provide the opportunity to measure physical stellar parameters such as
effective temperatures and metallicities for many of these stars. At the
culmination of this survey, we will have obtained multi-epoch spectra and RVs
for over 1400 stars spanning spectral types of M0-L0, providing the largest set
of NIR M dwarf spectra at high resolution, and more than doubling the number of
known spectroscopic vsini values for M dwarfs. Furthermore, by modeling
telluric lines to correct for small instrumental radial velocity shifts, we
hope to achieve a relative velocity precision floor of 50 m/s for bright M
dwarfs. We present preliminary results of this telluric modeling technique in
this paper.Comment: Submitted to Astronomical Journa
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The SDSS-III APOGEE Radial Velocity Survey Of M Dwarfs. I. Description Of The Survey And Science Goals
We are carrying out a large ancillary program with the Sloan Digital Sky Survey, SDSS-III, using the fiber-fed multi-object near-infrared APOGEE spectrograph, to obtain high-resolution H-band spectra of more than 1200 M dwarfs. These observations will be used to measure spectroscopic rotational velocities, radial velocities, physical stellar parameters, and variability of the target stars. Here, we describe the target selection for this survey, as well as results from the first year of scientific observations based on spectra that will be publicly available in the SDSS-III DR 10 data release. As part of this paper we present radial velocities and rotational velocities of over 200 M dwarfs, with a v sin i precision of similar to 2 km s(-1) a measurement floor at v sin i = 4 km s(-1). This survey significantly increases the number of M dwarfs studied for rotational velocities and radial velocity variability (at similar to 100-200 m s(-1)), and will inform and advance the target selection for planned radial velocity and photometric searches for low-mass exoplanets around M dwarfs, such as the Habitable Zone Planet Finder, CARMENES, and TESS. Multiple epochs of radial velocity observations enable us to identify short period binaries, and adaptive optics imaging of a subset of stars enables the detection of possible stellar companions at larger separations. The high-resolution APOGEE spectra, covering the entire H band, provide the opportunity to measure physical stellar parameters such as effective temperatures and metallicities for many of these stars. At the culmination of this survey, we will have obtained multi-epoch spectra and radial velocities for over 1400 stars spanning the spectral range M0-L0, providing the largest set of near-infrared M dwarf spectra at high resolution, and more than doubling the number of known spectroscopic a sin i values for M dwarfs. Furthermore, by modeling telluric lines to correct for small instrumental radial velocity shifts, we hope to achieve a relative velocity precision floor of 50 m s(-1) for bright M dwarfs. With three or more epochs, this precision is adequate to detect substellar companions, including giant planets with short orbital periods, and flag them for higher-cadence followup. We present preliminary, and promising, results of this telluric modeling technique in this paper.Center for Exoplanets and Habitable WorldsPennsylvania State UniversityEberly College of SciencePennsylvania Space Grant ConsortiumNSF AST 1006676, AST 1126413National Science FoundationNational Aeronautics and Space Administration NNX-08AE38A, NNX13AB03GAlfred P. Sloan FoundationU.S. Department of Energy Oce of ScienceUniversity of ArizonaBrazilian Participation GroupBrookhaven National LaboratoryUniversity of CambridgeCarnegie Mellon UniversityUniversity of FloridaFrench Participation GroupGerman Participation GroupHarvard UniversityInstituto de Astrosica de CanariasMichigan State/Notre Dame/JINA Participation GroupJohns Hopkins UniversityLawrence Berkeley National LaboratoryMax Planck Institute for AstrophysicsMax Planck Institute for Extraterrestrial PhysicsNew Mexico State UniversityNew York UniversityOhio State UniversityUniversity of PortsmouthPrinceton UniversitySpanish Participation GroupUniversity of TokyoUniversity of UtahVanderbilt UniversityUniversity of VirginiaUniversity of WashingtonYale UniversityMcDonald Observator
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