Publications (38)101.29 Total impact
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ABSTRACT: We study transients produced by equatorial disclike outflows from catastrophically masslosing binary stars with an asymptotic velocity and energy deposition rate near the inner edge which are proportional to the binary escape velocity vesc. As a test case, we present the first smoothedparticle radiationhydrodynamics calculations of the mass loss from the outer Lagrange point with realistic equation of state and opacities. The resulting spiral stream becomes unbound for binary mass ratios 0.06 ≲ q ≲ 0.8. For synchronous binaries with nondegenerate components, the spiralstream arms merge at a radius of ∼10a, where a is the binary semimajor axis, and the accompanying shock thermalizes about 10 per cent of the kinetic power of the outflow. The masslosing binary outflows produce luminosities reaching up to ∼106 L⊙ and effective temperatures spanning 500 ≲ Teff ≲ 6000 K, which is compatible with many of the class of recently discovered red transients such as V838 Mon and V1309 Sco. Dust readily forms in the outflow, potentially in a catastrophic global cooling transition. The appearance of the transient is viewing angledependent due to vastly different optical depths parallel and perpendicular to the binary plane. We predict a correlation between the peak luminosity and the outflow velocity, which is roughly obeyed by the known red transients. Outflows from masslosing binaries can produce luminous (105 L⊙) and cool (Teff ≲ 1500 K) transients lasting a year or longer, as has potentially been detected by Spitzer surveys of nearby galaxies.  [Show abstract] [Hide abstract]
ABSTRACT: Hydrogenrich Type IIPlateau supernovae are known to exhibit correlations between the plateau luminosity L_pl, the nickel mass M_Ni, the explosion energy E_exp, and the ejecta mass M_ej. Using our global, selfconsistent, multiband model of nearby wellobserved supernovae, we find that the uncertainty covariances of these quantities are significant and that the confidence ellipsoids are oriented in the direction of the correlations, which reduces their significance. By proper treatment of the covariance matrix of the model, we discover a significant intrinsic width to the correlations between L_pl, E_exp and M_Ni, where the uncertainties due to the distance and the extinction dominate. For fixed E_exp, the spread in M_Ni is about 0.25 dex, which we explain as differences in the progenitor internal structure. We argue that the effects of incomplete gammaray trapping are not important in our sample. Similarly, the physics of the Type IIPlateau supernova light curves leads to inherently degenerate estimates of E_exp and M_ej, which makes their observed correlation weak. Ignoring the covariances of supernova parameters or the intrinsic width of the correlations causes significant biases in the slopes and other parameters of the fitted relations. Our results imply that Type IIPlateau supernova explosions are not described by a single physical parameter or a simple onedimensional trajectory through the parameter space, but instead reflect the diversity of the core and surface properties of their progenitors. We discuss the implications for the physics of the explosion mechanism and possible future observational constraints. 
Article: Discovery and Observations of the Unusually Bright TypeDefying IIP/IIL Supernova ASASSN13co
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ABSTRACT: We present photometric and spectroscopic observations of ASASSN13co, an unusually luminous Type II supernova and the first corecollapse supernova discovered by the AllSky Automated Survey for SuperNovae (ASASSN). First detection of the supernova was on UT 2013 August 29 and the data presented span roughly 3.5 months after discovery. We use the recently developed model from Pejcha & Prieto (2014) to model the multiband light curves of ASASSN13co and derive the bolometric luminosity curve. We compare ASASSN13co to other Type II supernovae to show that it was a unique event that was not only unusually bright for a Type II supernova but also exhibited an atypical light curve shape that does not cleanly match that of either a standard Type IIL or Type IIP supernova.  [Show abstract] [Hide abstract]
ABSTRACT: A large reverberation mapping study of the Seyfert 1 galaxy NGC 7469 has yielded emissionline lags for Hbeta 4861 and He II 4686 and a central black hole mass measurement of about 10 million solar masses, consistent with previous measurements. A very low level of variability during the monitoring campaign precluded meeting our original goal of recovering velocitydelay maps from the data, but with the new Hbeta measurement, NGC 7469 is no longer an outlier in the relationship between the size of the Hbetaemitting broadline region and the AGN luminosity. It was necessary to detrend the continuum and Hbeta and He II 4686 line light curves and those from archival UV data for different timeseries analysis methods to yield consistent results.  [Show abstract] [Hide abstract]
ABSTRACT: We present a new selfconsistent and versatile method that derives photospheric radius and temperature variations of Type IIPlateau supernovae based on their expansion velocities and photometric measurements. We apply the method to a sample of 26 wellobserved, nearby supernovae with published light curves and velocities. We simultaneously fit ~230 velocity and ~6800 magnitude measurements distributed over 21 photometric passbands spanning wavelengths from 0.19 to 2.2 microns. We show that the light curve differences among the Type IIPlateau supernovae are wellmodeled by assuming different rates of photospheric radius expansion, which we explain as differences in the density profiles of the ejecta between supernovae. We argue that the steep luminosity decline of Type IILinear supernovae is due to fast evolution of the photospheric temperature, which we verify with a successful fit of SN1980K. Eliminating the need for theoretical supernova atmosphere models, we obtain selfconsistent relative distances, reddenings, and nickel masses fully accounting for all internal model uncertainties and covariances. We use our global fit to estimate the time evolution of any missing band tailored specifically for each supernova and we construct spectral energy distributions and bolometric light curves. We produce bolometric corrections for all filter combinations in our sample. We compare our model to the theoretical dilution factors and find good agreement for the B and V filters. Our results differ from the theory when the I, J, H, or K bands are included. We investigate the reddening law towards our supernovae and find reasonable agreement with standard R_V ~ 3.1 reddening law in UBVRI bands. Results for other bands are inconclusive.  [Show abstract] [Hide abstract]
ABSTRACT: If the neutrino luminosity from the protoneutron star formed during a massive star core collapse exceeds a critical threshold, a supernova (SN) results. The normalization of this critical threshold and its dependencies on the parameters of the system remain uncertain. Using spherical quasistatic evolutionary sequences for many hundreds of progenitors over a wide range of metallicities, we study how the explosion threshold maps onto observables  (1) fraction of successful explosions, (2) remnant neutron star (NS) and black hole (BH) mass functions, (3) explosion energies (E_SN), (4) nickel yields (M_Ni)  and their mutual correlations. We show that the neutrino mechanism can in principle explain the observed properties of SNe and the compact objects they produce. Successful explosions are intertwined with failures in a complex but welldefined pattern that is not well described by the progenitor initial mass and is not simply related to compactness. In the context of singlestar progenitors, we show that the neutrino mechanism predicts that at solar metallicity, initial masses of 15+/1, 19+/1, and 2126 M_Sun are most likely to form BHs, that the BH formation probability is significantly higher for low metallicity progenitors, and that low luminosity, low M_Ni SNe come from progenitors close to success/failure interfaces. We qualitatively reproduce the correlation between E_SN and M_Ni and we predict a correlation between both the mean and width of the NS mass distribution and E_SN distribution. We use the observed properties of NSs, BHs, and SN explosions to study the likelihood of many parameterizations of the neutrino mechanism. We find a distinct region of high probability favoring the existence of failed supernovae. We argue that the rugged landscape of progenitor structures mandates performing internally consistent simulations for large sets of progenitors. (Abridged)  [Show abstract] [Hide abstract]
ABSTRACT: We present the discovery of a Neptunemass planet OGLE2007BLG368Lb with a planetstar mass ratio of q = [9.5 ± 2.1] × 10–5 via gravitational microlensing. The planetary deviation was detected in realtime thanks to the high cadence of the Microlensing Observations in Astrophysics survey, realtime lightcurve monitoring and intensive followup observations. A Bayesian analysis returns the stellar mass and distance at Ml = 0.64+0.21–0.26M ☉ and Dl = 5.9+0.9–1.4 kpc, respectively, so the mass and separation of the planet are Mp = 20+7–8M ⊕ and a = 3.3+1.4–0.8 AU, respectively. This discovery adds another cold Neptunemass planet to the planetary sample discovered by microlensing, which now comprises four cold Neptune/superEarths, five gas giant planets, and another subSaturn mass planet whose nature is unclear. The discovery of these 10 cold exoplanets by the microlensing method implies that the mass ratio function of cold exoplanets scales as dN pl/dlog q ∝ q –0.7±0.2 with a 95% confidence level upper limit of n < –0.35 (where dN pl/dlog q ∝ qn). As microlensing is most sensitive to planets beyond the snowline, this implies that Neptunemass planets are at least three times more common than Jupiters in this region at the 95% confidence level.  [Show abstract] [Hide abstract]
ABSTRACT: We study the orbital evolution of hierarchical quadruple systems composed of two binaries on a long mutual orbit, where each binary acts as a KozaiLidov (KL) perturber on the other. We find that the coupling between the two binaries qualitatively changes the behavior of their KL cycles. The binaries can experience coherent eccentricity oscillations as well as excursions to very high eccentricity that occur over a much larger fraction of the parameter space than in triple systems. For a ratio of outer to inner semimajor axes of 10 to 20, about 30 to 50% of equalmass quadruples reach eccentricity 1e < 10^{3} in one of the binaries. This is about 4 to 12 times more than for triples with equivalent parameters. Orbital "flips" and collisions without previous tidal interaction are similarly enhanced in quadruples relative to triples. We argue that the frequency of evolutionary paths influenced by KL cycles is comparable in the triple and quadruple populations even though field quadruples are a factor of ~5 less frequent than triples. Additionally, quadruples might be a nonnegligible source of triples and provide fundamentally new evolutionary outcomes involving close binaries, mergers, collisions, and associated transients, which occur without any fine tuning of parameters. Finally, we study the perturbations to a planetary orbit due to a distant binary and we find that the fraction of orbital flips is a factor of 3 to 4 higher than for the corresponding triple system given our fiducial parameters with implications for hot Jupiters and starplanet collisions.  [Show abstract] [Hide abstract]
ABSTRACT: We present velocityresolved reverberation results for five active galactic nuclei. We recovered velocitydelay maps using the maximum entropy method for four objects: Mrk 335, Mrk 1501, 3C 120, and PG 2130+099. For the fifth, Mrk 6, we were only able to measure mean time delays in different velocity bins of the Hβ emission line. The four velocitydelay maps show unique dynamical signatures for each object. For 3C 120, the Balmer lines show kinematic signatures consistent with both an inclined disk and infalling gas, but the He II λ4686 emission line is suggestive only of inflow. The Balmer lines in Mrk 335, Mrk 1501, and PG 2130+099 show signs of infalling gas, but the He II emission in Mrk 335 is consistent with an inclined disk. We also see tentative evidence of combined virial motion and infalling gas from the velocitybinned analysis of Mrk 6. The maps for 3C 120 and Mrk 335 are two of the most clearly defined velocitydelay maps to date. These maps constitute a large increase in the number of objects for which we have resolved velocitydelay maps and provide evidence supporting the reliability of reverberationbased black hole mass measurements.  [Show abstract] [Hide abstract]
ABSTRACT: We present velocityresolved reverberation results for five active galactic nuclei. We recovered velocitydelay maps using the maximumentropy method for four objects: Mrk 335, Mrk 1501, 3C120, and PG2130+099. For the fifth, Mrk 6, we were only able to measure mean time delays in different velocity bins of the Hbeta emission line. The four velocitydelay maps show unique dynamical signatures for each object. For 3C120, the Balmer lines show kinematic signatures consistent with both an inclined disk and infalling gas, but the HeII 4686 emission line is suggestive only of inflow. The Balmer lines in Mrk 335, Mrk 1501, and PG 2130+099 show signs of infalling gas, but the HeII emission in Mrk 335 is consistent with an inclined disk. We also see tentative evidence of combined virial motion and infalling gas from the velocitybinned analysis of Mrk 6. The maps for 3C120 and Mrk 335 are two of the most clearly defined velocitydelay maps to date. These maps constitute a large increase in the number of objects for which we have resolved velocitydelay maps and provide evidence supporting the reliability of reverberationbased black hole mass measurements.  [Show abstract] [Hide abstract]
ABSTRACT: We present the results from a detailed analysis of photometric and spectrophotometric data on five Seyfert 1 galaxies observed as a part of a recent reverberation mapping program. The data were collected at several observatories over a 140 day span beginning in 2010 August and ending in 2011 January. We obtained high samplingrate light curves for Mrk 335, Mrk 1501, 3C 120, Mrk 6, and PG 2130+099, from which we have measured the time lag between variations in the 5100 Å continuum and the Hβ broad emission line. We then used these measurements to calculate the mass of the supermassive black hole at the center of each of these galaxies. Our new measurements substantially improve previous measurements of M BH and the size of the broad lineemitting region for four sources and add a measurement for one new object. Our new measurements are consistent with photoionization physics regulating the location of the broad line region in active galactic nuclei.  [Show abstract] [Hide abstract]
ABSTRACT: The evolution of multiple stellar systems can be driven by Kozai cycles and tidal friction (KCTF), which shrink the orbit of the inner binary. There is an interesting possibility that two close binaries on a common longperiod orbit experience mutuallyinduced KCTF. We present the discovery of a possible new quadruple system composed of two unresolved eclipsing binaries (EBs), CzeV343 (V~13.5 mag). We obtained photometric observations of CzeV343 that completely cover the two orbital periods and we successfully model the light curves as the sum of two detached EBs. We provide confidence intervals for the model parameters and minima timings by bootstrap resampling of our data. One of the EBs shows a distinctly eccentric orbit with a total eccentricity of about 0.18. The two orbital periods, 1.20937 and 0.80693 days, are within 0.1% of a 3:2 ratio. We speculate that this might be the result of KCTFdriven evolution of a quadruple system and we discuss this hypothesis in the context of other quadruple systems composed of two EBs. We make our double EB fitting code publicly available to provide a tool for longterm monitoring of the mutual orbit in such systems.  [Show abstract] [Hide abstract]
ABSTRACT: Differential photometric measurements of CzeV343 obtained with 0.25m Newtonian telescope with G416000 and G23200 CCD cameras are presented. The photometry is mostly without any photometric filter, although some measurements in V and I were obtained as well. For each measurement, we give Julian date, differential magnitude with respect to a comparison star, photometric error and modeled magnitude. (1 data file). 
Article: Double Eclipsing Binary Fitting
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ABSTRACT: The parameters of the mutual orbit of eclipsing binaries that are physically connected can be obtained by precision timing of minima over time through light travel time effect, apsidal motion or orbital precession. This, however, requires joint analysis of data from different sources obtained through various techniques and with insufficiently quantified uncertainties. In particular, photometric uncertainties are often underestimated, which yields too small uncertainties in minima timings if determined through analysis of a ?2 surface. The task is even more difficult for double eclipsing binaries, especially those with periods close to a resonance such as CzeV344, where minima get often blended with each other. This code solves the double binary parameters simultaneously and then uses these parameters to determine minima timings (or more specifically OC values) for individual datasets. In both cases, the uncertainties (or more precisely confidence intervals) are determined through bootstrap resampling of the original data. This procedure to a large extent alleviates the common problem with underestimated photometric uncertainties and provides a check on possible degeneracies in the parameters and the stability of the results. While there are shortcomings to this method as well when compared to Markov Chain Monte Carlo methods, the ease of the implementation of bootstrapping is a significant advantage. 
Article: The observed neutron star mass distribution as a probe of the supernova explosion mechanism
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ABSTRACT: The observed distribution of neutron star (NS) masses reflects the physics of corecollapse supernova explosions and the structure of the massive stars that produce them at the end of their evolution. We present a Bayesian analysis that directly compares the NS mass distribution observed in double NS systems to theoretical models of NS formation. First, we find that models with standard binary mass ratio distributions are strongly preferred over independently picking the masses from the initial mass function, although the strength of the inference depends on whether current assumptions for identifying the remnants of the primary and secondary stars are correct. Secondly, NS formation models with no mass fallback are favoured because they reduce the dispersion in NS masses. The double NS system masses thus directly point to the mass coordinate where the supernova explosion was initiated, making them an excellent probe of the supernova explosion mechanism. If we assume no fallback and simply vary the mass coordinate separating the remnant and the supernova ejecta, we find that for solar metallicity stars the explosion most likely develops at the edge of the iron core at a specific entropy of S/NA≈ 2.8 kB. The primary limitations of our study are the poor knowledge of the supernova explosion mechanism and the lack of broad range of supernova model explosions of Large Magellanic Cloud to solar metallicity. 
Article: A Global Physical Model for Cepheids
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ABSTRACT: We perform a global fit to ~5,000 radial velocity and ~177,000 magnitude measurements in 29 photometric bands covering 0.3 to 8.0 microns distributed among 287 Galactic, LMC, and SMC Cepheids with P > 10 days. We assume that the Cepheid light curves and radial velocities are fully characterized by distance, reddening, and timedependent radius and temperature variations. We construct phase curves of radius and temperature for periods between 10 and 100 days, which yield light curve templates for all our photometric bands and can be easily generalized to any additional band. With only 4 to 6 parameters per Cepheid, depending on the existence of velocity data and the amount of freedom in the distance, the models have typical rms light and velocity curve residuals of 0.05 mag and 3.5 km/s. The model derives the mean Cepheid spectral energy distribution and its derivative with respect to temperature, which deviate from a black body in agreement with metalline and molecular opacity effects. We determine a mean reddening law towards the Cepheids in our sample, which is not consistent with standard assumptions in either the optical or nearIR. Based on stellar atmosphere models we predict the biases in distance, reddening, and temperature determinations due to the metallicity and we quantify the metallicity signature expected for our fit residuals. The observed residuals as a function of wavelength show clear differences between the individual galaxies, which are compatible with these predictions. In particular, we find that metalpoor Cepheids appear hotter. Finally, we provide a framework for optimally selecting filters that yield the smallest overall errors in Cepheid parameter determination, or filter combinations for suppressing or enhancing the metallicity effects on distance determinations. We make our templates publicly available.  [Show abstract] [Hide abstract]
ABSTRACT: We present the first results from a detailed analysis of photometric and spectrophotometric data on the narrowline Seyfert 1 galaxy Mrk 335, collected over a 120day span in the fall of 2010. From these data we measure the lag in the He II 4686 broad emission line relative to the optical continuum to be 2.7 \pm 0.6 days and the lag in the H\beta 4861 broad emission line to be 13.9 \pm 0.9 days. Combined with the line width, the He II lag yields a black hole mass, MBH = (2.6 \pm 0.8)\times 10^7 Msun. This measurement is consistent with measurements made using the H\beta 4861 line, suggesting that the He II emission originates in the same region as H\beta, but at a much smaller radius. This constitutes the first robust lag measurement for a highionization line in a narrowline Seyfert 1 galaxy.  [Show abstract] [Hide abstract]
ABSTRACT: The data were obtained on the MDM 1.3m McGrawHill telescope using the 4K imager. The observations consist of 60s exposures taken through the Cousins R filter and 10s exposures taken through the Cousins I filter. The data were collected over 19 nights during the fall of 2007, spanning September 12October 24, and 18 nights during the summer of 2009, spanning May 30June 25. (1 data file). 
Article: Effect of Collective Neutrino Oscillations on the Neutrino Mechanism of CoreCollapse Supernovae
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ABSTRACT: In the seconds after collapse of a massive star, the newborn protoneutron star (PNS) radiates neutrinos of all flavours. The absorption of electrontype neutrinos below the radius of the stalled shockwave may drive explosions (the ‘neutrino mechanism’). Because the heating rate is proportional to the square of neutrino energy, flavour conversion of μ and τ neutrinos to electrontype neutrinos via collective neutrino oscillations (CνO) may in principle increase the heating rate and drive explosions. In order to assess the potential importance of CνO for the shock revival, we solve the steadystate boundary value problem of spherically symmetric accretion between the PNS surface (rν) and the shock (rS), including a scheme for flavour conversion via CνO. For a given rν, PNS mass (M), accretion rate () and assumed values of the neutrino energies from the PNS, we calculate the critical neutrino luminosity above which accretion is impossible and explosion results. We show that CνO can decrease the critical luminosity by a factor of at most ∼1.5, but only if the flavour conversion is fully completed inside rS and if there is no matter suppression. The magnitude of the effect depends on the model parameters (M, and rν) through the shock radius and the physical scale for flavour conversion. We quantify these dependencies and find that CνO could lower the critical luminosity only for small M and , and large rν. However, for these parameter values CνO are suppressed due to matter effects. By quantifying the importance of CνO and matter suppression at the critical neutrino luminosity for explosion, we show in agreement with previous studies that CνO are unlikely to affect the neutrino mechanism of corecollapse supernovae significantly.  [Show abstract] [Hide abstract]
ABSTRACT: (Abridged) Neutrino heating may drive corecollapse supernova explosions. Although it is known that the stalled accretion shock turns into explosion when the neutrino luminosity from the collapsed core exceeds a critical value (L_crit) (the "neutrino mechanism"), the physics of L_crit, as well as its dependence on the properties of the protoneutron star (PNS) and changes to the microphysics has never been systematically explored. We solve the onedimensional steadystate accretion problem between the PNS surface and the accretion shock. We quantify the deep connection between the solution space of steadystate accretion flows with bounding shocks and the neutrino mechanism. We show that there is a maximum, critical sound speed above which it is impossible to maintain accretion with a standoff shock, because the shock jump conditions cannot be satisfied. The physics of this critical sound speed is general and does not depend on a specific heating mechanism. For the simple model of pressureless freefall onto a shock bounding an isothermal accretion flow with sound speed c_T, we show that if c_T^2/v_escape^2 > 3/16 explosion results. We generalize this result to the more complete supernova problem, showing explicitly that the same physics determines L_crit. We find that the critical condition for explosion can be written as c_S^2/v_escape^2 = 0.19, where c_S is the adiabatic sound speed. This "antesonic" condition describes L_crit over a broad range in accretion rate and microphysics. We show that the addition of the accretion luminosity (L_acc) reduces L_crit nontrivially. As in previous work, we find that L_crit is always significantly higher than the maximum possible value of L_acc. Finally, we provide evidence that the reduction in L_crit seen in recent multidimensional simulations results from a reduction in the efficiency of cooling, rather than an increase in the heating rate.
Publication Stats
340  Citations  
101.29  Total Impact Points  
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Institutions

20142015

Princeton University
Princeton, New Jersey, United States


20102014

The Ohio State University
 Department of Astronomy
Columbus, Ohio, United States
