66 research outputs found
Superflares and Giant Planets
Stellar flares 100-10^7 times more energetic than the most powerful solar
flares have been detected from 9 normal F and G main sequence stars (Schaefer,
King & Deliyannis 2000). Although these stars are not in close binary systems,
their superflares show a remarkable similarity to the large stellar flares
observed on RS Canum Venaticorum binary systems. Such flares are caused by
magnetic reconnection events associated with the tangling of magnetic fields
between the two stars. The superflare stars are certainly not of this class,
although the mechanism may be similar. The superflares may be caused by
magnetic reconnection between fields of the primary star and a close-in Jovian
planet. This scenario explains the energies, durations, and spectra of
superflares, as well as explain why our Sun does not have such events. Only
known planetary properties and reconnection scenarios are required by this
mechanism.Comment: 8 pages, 8 figures. High resolution PDF available from
http://www.astro.yale.edu/ericr
HST Observations of the Central-Cusp Globular Cluster NGC 6752. The Effect of Binary Stars on the Luminosity Function in the Core
We consider the effect of binary stars on the main-sequence luminosity
functions observed in the core of globular clusters, with specific reference to
NGC 6752. We find that mass segregation results in an increased binary fraction
at fainter magnitudes along the main-sequence. If this effect is not taken into
account when analyzing luminosity functions, erroneous conclusions can be drawn
regarding the distribution of single stars, and the dynamical state of the
cluster. In the core of NGC 6752, our HST data reveal a flat luminosity
function, in agreement with previous results. However, when we correct for the
increasing binary fraction at faint magnitudes, the LF begins to fall
immediately below the turn-off. This effect appears to be confined to the inner
core radius of the cluster.Comment: 10 pages, 3 figures Accepted to ApJ Lett Vol 513 Number
Are superflares on solar analogues caused by extra-solar planets?
Stellar flares with times more energy than the largest solar
flare have been detected from 9 normal F and G main sequence stars (Schaefer,
King & Deliyannis 1999). These superflares have durations of hours to days and
are visible from at least x-ray to optical frequencies. The absence of
world-spanning aurorae in historical records and of anomalous extinctions in
the geological record indicate that our Sun likely does not suffer superflares.
In seeking to explain this new phenomenon, we are struck by its similarity to
large stellar flares on RS Canum Venaticorum binary systems, which are caused
by magnetic reconnection events associated with the tangling of magnetic fields
between the two stars. The superflare stars are certainly not of this class,
although we propose a similar flare mechanism. That is, superflares are caused
by magnetic reconnection between fields of the primary star and a close-in
Jovian planet. Thus, by only invoking known planetary properties and
reconnection scenarios, we can explain the energies, durations, and spectra of
superflares, as well as explain why our Sun does not have such events.Comment: 13 pages, Accepted for publication in Ap
The Luminous Type Ic SN 1992ar at z=0.145
We present spectroscopic and photometric observations of SN1992ar, the more
distant SN in the Calan/Tololo Survey. We compare its spectrum with those of
nearby Type Ia and Ic SNe and conclude that the latter type is a better match
to SN 1992ar. Using K-corrections based on the spectra of well observed Type Ic
and Ia SNe we compute different possible rest frame light curves of SN 1992ar
and compare them with those of representative SNe of each type observed in the
nearby universe. From the photometry and the spectra, we are able to conclude
that SN 1992ar cannot be matched by any known example of a Type Ia SN. Even
though the data set collected is fairly complete (one spectrum and 10
photometric points), it is not possible to decide whether SN 1992ar was a fast
Type Ic SN, like SN 1994I, or a slow one, like SN 1983V. The absolute V
magnitudes at maximum implied by each of these possibilities are -19.2 and
-20.2, respectively. The latter would make SN 1992ar one of the brightest SNe
on record. SN 1992ar, hence, illustrates the problem of contamination faced by
the high z Type Ia SNe samples whose luminosity distances are used to determine
the cosmological parameters of the Universe. We present observational criteria
to distinguish the two SN types when the SiII 6355 line is redshifted out of
the sensitivity range of typical CCD detectors, and discuss the effect that
these luminous Type Ic SNe would have on the measured cosmological parameters,
if not removed from the High-z Type Ia SN samples.Comment: 40 pages, 9 figures. Accepted for publication in Astrophysical
Journa
QMCPACK: Advances in the development, efficiency, and application of auxiliary field and real-space variational and diffusion Quantum Monte Carlo
We review recent advances in the capabilities of the open source ab initio
Quantum Monte Carlo (QMC) package QMCPACK and the workflow tool Nexus used for
greater efficiency and reproducibility. The auxiliary field QMC (AFQMC)
implementation has been greatly expanded to include k-point symmetries,
tensor-hypercontraction, and accelerated graphical processing unit (GPU)
support. These scaling and memory reductions greatly increase the number of
orbitals that can practically be included in AFQMC calculations, increasing
accuracy. Advances in real space methods include techniques for accurate
computation of band gaps and for systematically improving the nodal surface of
ground state wavefunctions. Results of these calculations can be used to
validate application of more approximate electronic structure methods including
GW and density functional based techniques. To provide an improved foundation
for these calculations we utilize a new set of correlation-consistent effective
core potentials (pseudopotentials) that are more accurate than previous sets;
these can also be applied in quantum-chemical and other many-body applications,
not only QMC. These advances increase the efficiency, accuracy, and range of
properties that can be studied in both molecules and materials with QMC and
QMCPACK
Optical Photometry of the Type Ia SN 1999ee and the Type Ib/c SN 1999ex in IC 5179
We present UBVRIz lightcurves of the Type Ia SN 1999ee and the Type Ib/c SN
1999ex, both located in the galaxy IC 5179. SN 1999ee has an extremely well
sampled lightcurve spanning from 10 days before Bmax through 53 days after
peak. Near maximum we find systematic differences ~0.05 mag in photometry
measured with two different telescopes, even though the photometry is reduced
to the same local standards around the supernova using the specific color terms
for each instrumental system. We use models for our bandpasses and
spectrophotometry of SN 1999ee to derive magnitude corrections (S-corrections)
and remedy this problem. This exercise demonstrates the need of accurately
characterizing the instrumental system before great photometric accuracies of
Type Ia supernovae can be claimed. It also shows that this effect can have
important astrophysical consequences since a small systematic shift of 0.02 mag
in the B-V color can introduce a 0.08 mag error in the extinction corrected
peak B magnitudes of a supernova and thus lead to biased cosmological
parameters. The data for the Type Ib/c SN 1999ex present us with the first ever
observed shock breakout of a supernova of this class. These observations show
that shock breakout occurred 18 days before Bmax and support the idea that Type
Ib/c supernovae are due to core collapse of massive stars rather than
thermonuclear disruption of white dwarfs.Comment: 55 pages, 15 figures, accepted by the Astronomical Journa
BVRI Light Curves for 29 Type Ia Supernovae
BVRI light curves are presented for 27 Type Ia supernovae discovered during
the course of the Calan/Tololo Survey and for two other SNe Ia observed during
the same period. Estimates of the maximum light magnitudes in the B, V, and I
bands and the initial decline rate parameter m15(B) are also given.Comment: 17 pages, figures and tables are not included (contact first author
if needed), to appear in the Astronomical Journa
Optical and Infrared Photometry of the Type Ia Supernovae 1991T, 1991bg, 1999ek, 2001bt, 2001cn, 2001cz, and 2002bo
We present optical and/or infrared photometry of the Type Ia supernovae SN
1991T, SN 1991bg, SN 1999ek, SN 2001bt, SN 2001cn, SN 2001cz, and SN 2002bo.
All but one of these supernovae have decline rate parameters Delta m_15(B)
close to the median value of 1.1 for the whole class of Type Ia supernovae. The
addition of these supernovae to the relationship between the near-infrared
absolute magnitudes and Delta m_15(B) strengthens the previous relationships we
have found, in that the maximum light absolute magnitudes are essentially
independent of the decline rate parameter. (SN 1991bg, the prototype of the
subclass of fast declining Type Ia supernovae, is a special case.) The
dispersion in the Hubble diagram in JHK is only ~0.15 mag. The near-infrared
properties of Type Ia supernovae continue to be excellent measures of the
luminosity distances to the supernova host galaxies, due to the need for only
small corrections from the epoch of observation to maximum light, low
dispersion in absolute magnitudes at maximum light, and the minimal reddening
effects in the near-infrared.Comment: Astron. J., 128, 3034 (Dec. 2004). This version with updated author
list, addresses, acknowledgments, reference
On the interpretation of removable interactions: A survey of the field 33Â years after Loftus
In a classic 1978 Memory &Cognition article, Geoff Loftus explained why noncrossover interactions are removable. These removable interactions are tied to the scale of measurement for the dependent variable and therefore do not allow unambiguous conclusions about latent psychological processes. In the present article, we present concrete examples of how this insight helps prevent experimental psychologists from drawing incorrect conclusions about the effects of forgetting and aging. In addition, we extend the Loftus classification scheme for interactions to include those on the cusp between removable and nonremovable. Finally, we use various methods (i.e., a study of citation histories, a questionnaire for psychology students and faculty members, an analysis of statistical textbooks, and a review of articles published in the 2008 issue of Psychology andAging) to show that experimental psychologists have remained generally unaware of the concept of removable interactions. We conclude that there is more to interactions in a 2 × 2 design than meets the eye
Effect of VX-770 in Persons with Cystic Fibrosis and the G551D- CFTR Mutation
A new approach in the treatment of cystic fibrosis involves improving the function of mutant cystic fibrosis transmembrane conductance regulator (CFTR). VX-770, a CFTR potentiator, has been shown to increase the activity of wild-type and defective cell-surface CFTR in vitro
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