205 research outputs found
A New Method to Calibrate the Magnitudes of Type Ia Supernovae at Maximum Light
We present a new empirical method for fitting multicolor light curves of Type
Ia supernovae. Our method combines elements from two widely used techniques in
the literature: the delta_m15 template fitting method and the Multicolor
Light-Curve Shape method. An advantage of our technique is the ease of adding
new colors, templates, or parameters to the fitting procedure. We use a large
sample of published light curves to calibrate the relations between the
absolute magnitudes at maximum and delta_m15 in BVRI filters. We find that
individual subsamples from a given survey or publication have significantly
tighter relationships between light curve shape and luminosity than the
relationship derived from the sum of all the samples, pointing to uncorrected
systematic errors in the photometry, mainly in BV filters. Using our method, we
calculate luminosity distances and host galaxy reddening to 89 SNe in the
Hubble flow and construct a low-z Hubble diagram. The dispersion of the SNe in
the Hubble diagram is 0.20 mag, or an error of ~9% in distance to a single SN.
Our technique produces similar or smaller dispersion in the low-z Hubble
diagram than other techniques in the literature.Comment: 43 pages, 16 figures, 6 tables, accepted by ApJ. For additional
material go to
http://www.astronomy.ohio-state.edu/~prieto/paper_dm15/dm15.htm
The Meyer-Neldel rule for a property determined by two transport mechanisms
We propose that the Meyer-Neldel rule (MNR) arises naturally for a quantity where both an intrinsic process as well as a process involving impurities contribute. The strength of the latter depends solely on the density of the impurities. This leads to a spread in the apparent activation energy of the measured quantity and the observation of the MNR, even though the intrinsic processes have fixed activation energies. A consequence of the MNR is the occurrence of a temperature T[sub MN] where a measured parameter is independent of the activation energy. For the system studied, the MNR does not accurately predict the results at temperatures larger than T[sub MN]. Our model for the MNR is supported by experimental data and it also can explain the inverse MNR for low activation energies
Meyer-Neldel rule for dark current in charge-coupled devices
We present the results of a systematic study of the dark current in each pixel of a charged-coupled device chip. It was found that the Arrhenius plot, at temperatures between 222 and 291 K, deviated from a linear behavior in the form of continuous bending. However, as a first approximation, the dark current, D, can be expressed as: D=Dₒ exp(−ΔE/kT),where ΔE is the activation energy, k is Boltzmann’s constant, and T the absolute temperature. It was found that ΔE and the exponential prefactor Dₒ follow the Meyer–Neldel rule (MNR) for all of the more than 222,000 investigated pixels. The isokinetic temperature, Tₒ, for the process was found as 294 K. However, measurements at 313 K did not show the predicted inversion in the dark current. It was found that the dark current for different pixels merged at temperatures higher than Tₒ. A model is presented which explains the nonlinearity and the merging of the dark current for different pixels with increasing temperature. Possible implications of this finding regarding the MNR are discussed
Late-Time Photometry of Type Ia Supernova SN 2012cg Reveals the Radioactive Decay of Co
Seitenzahl et al. (2009) have predicted that roughly three years after its
explosion, the light we receive from a Type Ia supernova (SN Ia) will come
mostly from reprocessing of electrons and X-rays emitted by the radioactive
decay chain , instead of positrons from the
decay chain that dominates the SN light at
earlier times. Using the {\it Hubble Space Telescope}, we followed the light
curve of the SN Ia SN 2012cg out to days after maximum light. Our
measurements are consistent with the light curves predicted by the contribution
of energy from the reprocessing of electrons and X-rays emitted by the decay of
Co, offering evidence that Co is produced in SN Ia explosions.
However, the data are also consistent with a light echo mag fainter
than SN 2012cg at peak. Assuming no light-echo contamination, the mass ratio of
Ni and Ni produced by the explosion, a strong constraint on any
SN Ia explosion model, is , roughly twice Solar. In
the context of current explosion models, this value favors a progenitor white
dwarf with a mass near the Chandrasekhar limit.Comment: Updated to reflect the final version published by ApJ. For a video
about the paper, see https://youtu.be/t3pUbZe8wq
The Unusual Variability of the Large Magellanic Cloud Planetary Nebula RPJ 053059-683542
We present images and light curves of the bipolar Planetary Nebula RPJ
053059-683542 that was discovered in the Reid-Parker AAO/UKST H-alpha survey of
the Large Magellanic Cloud (LMC). The emission from this object appears
entirely nebular, with the central star apparently obscured by a central band
of absorption that bisects the nebula. The light curves, which were derived
from images from the SuperMACHO project at CTIO, showed significant, spatially
resolved variability over the period 2002 January through 2005 December.
Remarkably, the emission from the two bright lobes of the nebula vary either
independently, or similarly but with a phase lag of at least one year. The
optical spectra show a low level of nebular excitation, and only modest N
enrichment. Infrared photometry from the 2MASS and SAGE surveys indicates the
presence of a significant quantity of dust. The available data imply that the
central star has a close binary companion, and that the system has undergone
some kind of outburst event that caused the nebular emission to first brighten
and then fade. Further monitoring, high-resolution imaging, and detailed IR
polarimetry and spectroscopy would uncover the nature of this nebula and the
unseen ionizing source.Comment: Accepted for ApJ Letters; 6 page
Residual images in charged-coupled device detectors
We present results of a systematic study of persistent, or residual, images that occur in charged-coupled device (CCD) detectors. A phenomenological model for these residual images, also known as ghosting, is introduced. This model relates the excess dark current in a CCD after exposure to the number of filled impurity sites which is tested for various temperatures and exposure times. We experimentally derive values for the cross section, density, and characteristic energy of the impurity sites responsible for the residual images
Galaxy Cores as Relics of Black Hole Mergers
We investigate the hypothesis that the cores of elliptical galaxies and
bulges are created from the binding energy liberated by the coalescence of
supermassive binary black holes during galaxy mergers. Assuming that the
central density profiles of galaxies were initially steep power laws, we define
the ``mass deficit'' as the mass in stars that had to be removed from the
nucleus in order to produce the observed core. We use nonparametric
deprojection to compute the mass deficit in a sample of 35 early-type galaxies
with high-resolution imaging data. We find that the mass deficit correlates
well with the mass of the nuclear black hole, consistent with the predictions
of merger models. We argue that core sizes in halos of non-interacting dark
matter particles should be comparable to those observed in the stars.Comment: 5 pages, 2 postscript figures, uses emulateapj.sty. Accepted for
publication in Monthly Notices of the Royal Astronomical Societ
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