428 research outputs found
How long is a hillslope?
Hillslope length is a fundamental attribute of landscapes, intrinsically linked to drainage density, landslide hazard, biogeochemical cycling and hillslope sediment transport. Existing methods to estimate catchment average hillslope lengths include inversion of drainage density or identification of a break in slope–area scaling, where the hillslope domain transitions into the fluvial domain. Here we implement a technique which models flow from point sources on hilltops across pixels in a digital elevation model (DEM), based on flow directions calculated using pixel aspect, until reaching the channel network, defined using recently developed channel extraction algorithms. Through comparisons between these measurement techniques, we show that estimating hillslope length from plots of topographic slope versus drainage area, or by inverting measures of drainage density, systematically underestimates hillslope length. In addition, hillslope lengths estimated by slope–area scaling breaks show large variations between catchments of similar morphology and area. We then use hillslope length–relief structure of landscapes to explore nature of sediment flux operating on a landscape. Distinct topographic forms are predicted for end-member sediment flux laws which constrain sediment transport on hillslopes as being linearly or nonlinearly dependent on hillslope gradient. Because our method extracts hillslope profiles originating from every ridgetop pixel in a DEM, we show that the resulting population of hillslope length–relief measurements can be used to differentiate between linear and nonlinear sediment transport laws in soil mantled landscapes. We find that across a broad range of sites across the continental United States, topography is consistent with a sediment flux law in which transport is nonlinearly proportional to topographic gradient
Aberrant trafficking of NSCLC-associated EGFR mutants through the endocytic recycling pathway promotes interaction with Src@
500 Days of SN 2013dy: spectra and photometry from the ultraviolet to the infrared
SN 2013dy is a Type Ia supernova for which we have compiled an extraordinary
dataset spanning from 0.1 to ~ 500 days after explosion. We present 10 epochs
of ultraviolet (UV) through near-infrared (NIR) spectra with HST/STIS, 47
epochs of optical spectra (15 of them having high resolution), and more than
500 photometric observations in the BVrRiIZYJH bands. SN 2013dy has a broad and
slowly declining light curve (delta m(B) = 0.92 mag), shallow Si II 6355
absorption, and a low velocity gradient. We detect strong C II in our earliest
spectra, probing unburned progenitor material in the outermost layers of the SN
ejecta, but this feature fades within a few days. The UV continuum of SN
2013dy, which is strongly affected by the metal abundance of the progenitor
star, suggests that SN 2013dy had a relatively high-metallicity progenitor.
Examining one of the largest single set of high-resolution spectra for a SN Ia,
we find no evidence of variable absorption from circumstellar material.
Combining our UV spectra, NIR photometry, and high-cadence optical photometry,
we construct a bolometric light curve, showing that SN 2013dy had a maximum
luminosity of 10.0^{+4.8}_{-3.8} * 10^{42} erg/s. We compare the synthetic
light curves and spectra of several models to SN 2013dy, finding that SN 2013dy
is in good agreement with a solar-metallicity W7 model.Comment: 22 pages, 18 figures, replaced with version accecpted for publication
in MNRA
Super-Earths: A New Class of Planetary Bodies
Super-Earths, a class of planetary bodies with masses ranging from a few
Earth-masses to slightly smaller than Uranus, have recently found a special
place in the exoplanetary science. Being slightly larger than a typical
terrestrial planet, super-Earths may have physical and dynamical
characteristics similar to those of Earth whereas unlike terrestrial planets,
they are relatively easier to detect. Because of their sizes, super-Earths can
maintain moderate atmospheres and possibly dynamic interiors with plate
tectonics. They also seem to be more common around low-mass stars where the
habitable zone is in closer distances. This article presents a review of the
current state of research on super-Earths, and discusses the models of the
formation, dynamical evolution, and possible habitability of these objects.
Given the recent advances in detection techniques, the detectability of
super-Earths is also discussed, and a review of the prospects of their
detection in the habitable zones of low-mass stars is presented.Comment: A (non-technical) review of the literature on the current state
ofresearch on super-Earths. The topics include observation, formation,
dynamical evolution, habitability, composition, interior dynamics, magnetic
field, atmosphere, and propsect of detection. The article has 44 pages, 27
figures, and 203 references. It has been accepted for publication in the
journal Contemporary Physics (2011
The Lick AGN Monitoring Project 2011: Spectroscopic Campaign and Emission-Line Light Curves
In the Spring of 2011 we carried out a 2.5 month reverberation mapping
campaign using the 3 m Shane telescope at Lick Observatory, monitoring 15
low-redshift Seyfert 1 galaxies. This paper describes the observations,
reductions and measurements, and data products from the spectroscopic campaign.
The reduced spectra were fitted with a multicomponent model in order to isolate
the contributions of various continuum and emission-line components. We present
light curves of broad emission lines and the AGN continuum, and measurements of
the broad H-beta line widths in mean and root-mean square (rms) spectra. For
the most highly variable AGNs we also measured broad H-beta line widths and
velocity centroids from the nightly spectra. In four AGNs exhibiting the
highest variability amplitudes, we detect anticorrelations between broad H-beta
width and luminosity, demonstrating that the broad-line region "breathes" on
short timescales of days to weeks in response to continuum variations. We also
find that broad H-beta velocity centroids can undergo substantial changes in
response to continuum variations; in NGC 4593 the broad H-beta velocity shifted
by ~250 km/s over a one-month duration. This reverberation-induced velocity
shift effect is likely to contribute a significant source of confusion noise to
binary black hole searches that use multi-epoch quasar spectroscopy to detect
binary orbital motion. We also present results from simulations that examine
biases that can occur in measurement of broad-line widths from rms spectra due
to the contributions of continuum variations and photon-counting noise.Comment: 33 pages, 28 figures, accepted for publication in ApJ Supplement
Serie
The Very Young Type Ia Supernova 2012cg: Discovery and Early-Time Follow-Up Observations
On 2012 May 17.2 UT, only 1.5 +/- 0.2 d after explosion, we discovered SN
2012cg, a Type Ia supernova (SN Ia) in NGC 4424 (d ~ 15 Mpc). As a result of
the newly modified strategy employed by the Lick Observatory SN Search, a
sequence of filtered images was obtained starting 161 s after discovery.
Utilizing recent models describing the interaction of SN ejecta with a
companion star, we rule out a ~1 M_Sun companion for half of all viewing angles
and a red-giant companion for nearly all orientations. SN 2012cg reached a
B-band maximum of 12.09 +/- 0.02 mag on 2012 June 2.0 and took ~17.3 d from
explosion to reach this, typical for SNe Ia. Our pre-maximum brightness
photometry shows a narrower-than-average B-band light curve for SN 2012cg,
though slightly overluminous at maximum brightness and with normal color
evolution (including some of the earliest SN Ia filtered photometry ever
obtained). Spectral fits to SN 2012cg reveal ions typically found in SNe Ia at
early times, with expansion velocities >14,000 km/s at 2.5 d past explosion.
Absorption from C II is detected early, as well as high-velocity components of
both Si II 6355 Ang. and Ca II. Our last spectrum (13.5 d past explosion)
resembles that of the somewhat peculiar SN Ia 1999aa. This suggests that SN
2012cg will have a slower-than-average declining light curve, which may be
surprising given the faster-than-average rising light curve.Comment: re-submitted to ApJL, 4 figures, 1 tabl
The Lick AGN Monitoring Project 2011: Reverberation Mapping of Markarian 50
The Lick AGN Monitoring Project 2011 observing campaign was carried out over
the course of 11 weeks in Spring 2011. Here we present the first results from
this program, a measurement of the broad-line reverberation lag in the Seyfert
1 galaxy Mrk 50. Combining our data with supplemental observations obtained
prior to the start of the main observing campaign, our dataset covers a total
duration of 4.5 months. During this time, Mrk 50 was highly variable,
exhibiting a maximum variability amplitude of a factor of 4 in the U-band
continuum and a factor of 2 in the H-beta line. Using standard
cross-correlation techniques, we find that H-beta and H-gamma lag the V-band
continuum by tau_cen = 10.64(-0.93,+0.82) and 8.43(-1.28,+1.30) days,
respectively, while the lag of He II 4686 is unresolved. The H-beta line
exhibits a symmetric velocity-resolved reverberation signature with shorter
lags in the high-velocity wings than in the line core, consistent with an
origin in a broad-line region dominated by orbital motion rather than infall or
outflow. Assuming a virial normalization factor of f=5.25, the virial estimate
of the black hole mass is (3.2+-0.5)*10^7 solar masses. These observations
demonstrate that Mrk 50 is among the most promising nearby active galaxies for
detailed investigations of broad-line region structure and dynamics.Comment: Accepted for publication in ApJ Letters. 6 pages, 4 figure
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