Browsing by Subject "star"

Now showing 1 - 18 of 18

Almost All Of Kepler's Multiple-Planet Candidates Are Planets
(2012-05) Lissauer, Jack J.; Marcy, Geoffrey W.; Rowe, Jason F.; Bryson, Stephen T.; Adams, Elisabeth; Buchhave, Lars A.; Ciardi, David R.; Cochran, William D.; Fabrycky, D. C.; Ford, Eric B.; Fressin, Francois; Geary, John; Gilliland, Ronald L.; Holman, Matthew J.; Howell, Steve B.; Jenkins, Jon M.; Kinemuchi, Karen; Koch, David G.; Morehead, Robert C.; Ragozzine, Darin; Seader, Shawn E.; Tanenbaum, Peter G.; Torres, Guillermo; Twicken, Joseph D.; Cochran, William D.
We present a statistical analysis that demonstrates that the overwhelming majority of Kepler candidate multiple transiting systems (multis) indeed represent true, physically associated transiting planets. Binary stars provide the primary source of false positives among Kepler planet candidates, implying that false positives should be nearly randomly distributed among Kepler targets. In contrast, true transiting planets would appear clustered around a smaller number of Kepler targets if detectable planets tend to come in systems and/or if the orbital planes of planets encircling the same star are correlated. There are more than one hundred times as many Kepler planet candidates in multi-candidate systems as would be predicted from a random distribution of candidates, implying that the vast majority are true planets. Most of these multis are multiple-planet systems orbiting the Kepler target star, but there are likely cases where (1) the planetary system orbits a fainter star, and the planets are thus significantly larger than has been estimated, or (2) the planets orbit different stars within a binary/multiple star system. We use the low overall false-positive rate among Kepler multis, together with analysis of Kepler spacecraft and ground-based data, to validate the closely packed Kepler-33 planetary system, which orbits a star that has evolved somewhat off of the main sequence. Kepler-33 hosts five transiting planets, with periods ranging from 5.67 to 41 days.
Black Hole Feedback On The First Galaxies
(2012-09) Jeon, M.; Pawlik, A. H.; Greif, T. H.; Glover, S. C. O.; Bromm, V.; Milosavljevic, M.; Klessen, R. S.; Jeon, Myoungwon; Pawlik, Andreas H.; Greif, Thomas H.; Glover, Simon C. O.; Bromm, Volker; Milosavljević, Miloš
We study how the first galaxies were assembled under feedback from the accretion onto a central black hole (BH) that is left behind by the first generation of metal-free stars through self-consistent, cosmological simulations. X-ray radiation from the accretion of gas onto BH remnants of Population III (Pop III) stars, or from high-mass X-ray binaries (HMXBs), again involving Pop III stars, influences the mode of second generation star formation. We track the evolution of the black hole accretion rate and the associated X-ray feedback starting with the death of the Pop III progenitor star inside a minihalo and following the subsequent evolution of the black hole as the minihalo grows to become an atomically cooling galaxy. We find that X-ray photoionization heating from a stellar-mass BH is able to quench further star formation in the host halo at all times before the halo enters the atomic cooling phase. X-ray radiation from a HMXB, assuming a luminosity close to the Eddington value, exerts an even stronger, and more diverse, feedback on star formation. It photoheats the gas inside the host halo, but also promotes the formation of molecular hydrogen and cooling of gas in the intergalactic medium and in nearby minihalos, leading to a net increase in the number of stars formed at early times. Our simulations further show that the radiative feedback from the first BHs may strongly suppress early BH growth, thus constraining models for the formation of supermassive BHs.
Characteristics Of Kepler Planetary Candidates Based On The First Data Set
(2011-02) Borucki, William J.; Koch, David G.; Basri, Gibor; Batalha, Natalie; Boss, Alan; Brown, Timothy M.; Caldwell, Douglas; Christensen-Dalsgaard, Jorgen; Cochran, William D.; DeVore, Edna; Dunham, Edward W.; Dupree, Andrea K.; Gautier, Thomas N., III; Geary, John C.; Gilliland, Ronald; Gould, Alan; Howell, Steve B.; Jenkins, Jon M.; Kjeldsen, Hans; Latham, David W.; Lissauer, Jack J.; Marcy, Geoffrey W.; Monet, David G.; Sasselov, Dimitar; Tarter, Jill; Charbonneau, David; Doyle, Laurance; Ford, Eric B.; Fortney, Jonathan; Holman, Matthew J.; Seager, Sara; Steffen, Jason H.; Welsh, William F.; Allen, Christopher; Bryson, Stephen T.; Buchhave, Lars; Chandrasekaran, Hema; Christiansen, Jessie L.; Ciardi, David; Clarke, Bruce D.; Dotson, Jessie L.; Endl, Michael; Fischer, Debra; Fressin, Francois; Haas, Michael; Horch, Elliott; Howard, Andrew; Isaacson, Howard; Kolodziejczak, Jeffery; Li, Jie; MacQueen, Phillip; Meibom, Soren; Prsa, Andrej; Quintana, Elisa V.; Rowe, Jason; Sherry, William; Tenenbaum, Peter; Torres, Guillermo; Twicken, Joseph D.; Van Cleve, Jeffrey; Walkowicz, Lucianne; Wu, Hayley; Cochran, William D.; Endl, Michael; MacQueen, Phillip J.
In the spring of 2009, the Kepler Mission commenced high-precision photometry on nearly 156,000 stars to determine the frequency and characteristics of small exoplanets, conduct a guest observer program, and obtain asteroseismic data on a wide variety of stars. On 2010 June 15, the Kepler Mission released most of the data from the first quarter of observations. At the time of this data release, 705 stars from this first data set have exoplanet candidates with sizes from as small as that of Earth to larger than that of Jupiter. Here we give the identity and characteristics of 305 released stars with planetary candidates. Data for the remaining 400 stars with planetary candidates will be released in 2011 February. More than half the candidates on the released list have radii less than half that of Jupiter. Five candidates are present in and near the habitable zone; two near super-Earth size, and three bracketing the size of Jupiter. The released stars also include five possible multi-planet systems. One of these has two Neptune-size (2.3 and 2.5 Earth radius) candidates with near-resonant periods.
Constraints on Circumstellar Material Around the Type Ia Supernova 2007af(1,2)
(2007-12) Simon, Joshua D.; Gal-Yam, Avishay; Penprase, Bryan E.; Li, Weidong; Quimby, Robert M.; Silverman, Jeffrey M.; Prieto, Carlos Allende; Wheeler, J. Craig; Filippenko, Alexei V.; Martinez, Irene T.; Beeler, Daniel J.; Patat, Ferdinando; Quimby, Robert M.; Prieto, Carlos Allende; Wheeler, J. Craig
Patat et al. recently inferred the existence of circumstellar material around a normal Type Ia supernova (SN Ia) for the first time, finding time-variable Na I D absorption lines in the spectrum of SN 2006X. We present high-resolution spectroscopy of the bright SN Ia 2007af at three epochs and search for variability in any of the Na D absorption components. Over the time range from 4 days before to 24 days after maximum light, we find that the host-galaxy Na D lines appear to be of interstellar rather than circumstellar origin and do not vary down to the level of 18 m angstrom (column density of 2 x 10(11) cm(-2)). We limit any circumstellar absorption lines to be weaker than similar to 10 m angstrom (6 x 10(10) cm(-2)). For the case of material distributed in spherically symmetric shells of radius similar to 10(16) cm surrounding the progenitor system, we place an upper limit on the shell mass of similar to(3 x 10(-8))/X M circle dot, where X is the Na ionization fraction. We also show that SN 2007af is a photometrically and spectroscopically normal SN Ia. Assuming that the variable Na D lines in SN 2006X came from circumstellar matter, we therefore conclude that either there is a preferred geometry for the detection of variable absorption components in SNe Ia, or SN 2007af and SN 2006X had different types of progenitor systems.
Discovery of the Transiting Planet Kepler-5B
(2010-04) Koch, David G.; Borucki, William J.; Rowe, Jason F.; Batalha, Natalie M.; Brown, Timothy M.; Caldwell, Douglas A.; Caldwell, John; Cochran, William D.; DeVore, Edna; Dunham, Edward W.; Dupree, Andrea K.; Gautier, Thomas N., III; Geary, John C.; Gilliland, Ron L.; Howell, Steve B.; Jenkins, Jon M.; Latham, David W.; Lissauer, Jack J.; Marcy, Geoff W.; Morrison, David; Tarter, Jill; Cochran, William D.
We present 44 days of high duty cycle, ultra precise photometry of the 13th magnitude star Kepler-5 (KIC 8191672, T(eff) = 6300 K, log g = 4.1), which exhibits periodic transits with a depth of 0.7%. Detailed modeling of the transit is consistent with a planetary companion with an orbital period of 3.548460 +/- 0.000032 days and a radius of 1.431(-0.052)(+0.041) R(J). Follow-up radial velocity measurements with the Keck HIRES spectrograph on nine separate nights demonstrate that the planet is more than twice as massive as Jupiter with a mass of 2.114(-0.059)(+0.056) M(J) and a mean density of 0.894 +/- 0.079 g cm(-3).
Discovery, Progenitor and Early Evolution of A Stripped Envelope Supernova iPTF13bvn
(2013-09) Cao, Yi; Kasliwal, Mansi M.; Arcavi, Iair; Horesh, Assaf; Hancock, Paul; Valenti, Stefano; Cenko, S. Bradley; Kulkarni, S. R.; Gal-Yam, Avishay; Gorbikov, Evgeny; Ofek, Eran O.; Sand, David; Yaron, Ofer; Graham, Melissa; Silverman, Jeffrey M.; Wheeler, J. Craig; Marion, G. H.; Walker, Emma S.; Mazzali, Paolo; Howell, D. Andrew; Li, K. L.; Kong, A. K. H.; Bloom, Joshua S.; Nugent, Peter E.; Surace, Jason; Masci, Frank; Carpenter, John; Degenaar, Nathalie; Gelino, Christopher R.; Silverman, Jeffrey M.; Wheeler, J. Craig; Marion, G. H.
The intermediate Palomar Transient Factory reports our discovery of a young supernova, iPTF13bvn, in the nearby galaxy, NGC 5806 (22.5 Mpc). Our spectral sequence in the optical and infrared suggests a Type Ib classification. We identify a blue progenitor candidate in deep pre-explosion imaging within a 2 sigma error circle of 80 mas (8.7 pc). The candidate has an M-B luminosity of -5.52 +/- 0.39 mag and a B-I color of 0.25 +/- 0.25 mag. If confirmed by future observations, this would be the first direct detection for a progenitor of a Type Ib. Fitting a power law to the early light curve, we find an extrapolated explosion date around 0.6 days before our first detection. We see no evidence of shock cooling. The pre-explosion detection limits constrain the radius of the progenitor to be smaller than a few solar radii. iPTF13bvn is also detected in centimeter and millimeter wavelengths. Fitting a synchrotron self-absorption model to our radio data, we find a mass-loading parameter of 1.3x10(12) g cm(-1). Assuming a wind velocity of 10(3) km s(-1), we derive a progenitor mass-loss rate of 3 x 10(-5) M-circle dot yr(-1). Our observations, taken as a whole, are consistent with a Wolf-Rayet progenitor of the supernova iPTF13bvn.
The Exceptionally Luminous Type Ia Supernova 2007If
(2010-06) Yuan, F.; Quimby, Robert M.; Wheeler, J. Craig; Vinko, Jozsef; Chatzopoulos, Emmanouil; Akerlof, C. W.; Kulkarni, S.; Miller, J. M.; McKay, T. A.; Aharonian, F.; Wheeler, J. Craig; Vinko, Jozsef; Chatzopoulos, Emmanouil
SN 2007if was the third over-luminous Type Ia supernova (SN Ia) detected after 2003fg and 2006gz. We present the photometric and spectroscopic observations of the SN and its host by ROTSE-III, HET, and Keck. From the H a line identified in the host spectra, we determine a redshift of 0.0736. At this distance, the SN reached an absolute magnitude of -20.4, brighter than any other SNe Ia ever observed. If the source of luminosity is radioactive decay, a large amount of radioactive nickel (similar to 1.5 M(circle dot)) is required to power the peak luminosity, more than can be produced realistically in a Chandrasekhar mass progenitor. Low expansion velocity, similar to that of 2003fg, is also measured around the maximum light. The observations may suggest that SN 2007if was from a massive white dwarf progenitor, plausibly exploding with mass well beyond 1.4 M(circle dot). Alternatively, we investigate circumstellar interaction that may contribute to the excess luminosity.
High Resolution Optical And NIR Spectra Of HBC 722
(2015-07) Lee, Jeong-Eun; Park, Sunkyung; Green, Joel D.; Cochran, William D.; Kang, Wonseok; Lee, Sang-Gak; Sung, Hyun-Il; Lee, Jeong-Eun; Green, Joel D.; Cochran, William D.
We present the results of high resolution (R >= 30,000) optical and near-IR spectroscopic monitoring observations of HBC 722, a recent FU Orionis object that underwent an accretion burst in 2010. We observed HBC 722 in the optical/near-IR with the Bohyunsan Optical Echelle Spectrograph, Hobby-Eberly Telescope-HRS, and Immersion Grating Infrared Spectrograph, at various points in the outburst. We found atomic lines with strongly blueshifted absorption features or P Cygni profiles, both evidence of a wind driven by the accretion. Some lines show a broad double-peaked absorption feature, evidence of disk rotation. However, the wind-driven and disk-driven spectroscopic features are anti-correlated in time; the disk features became strong as the wind features disappeared. This anti-correlation might indicate that the rebuilding of the inner disk was interrupted by the wind pressure during the first 2 years. The half-width at half-depth of the double-peaked profiles decreases with wavelength, indicative of the Keplerian rotation; the optical spectra with the disk feature are fitted by a G5 template stellar spectrum convolved with a rotation velocity of 70 km s(-1) while the near-IR disk features are fitted by a K5 template stellar spectrum convolved with a rotation velocity of 50 km s(-1). Therefore, the optical and near-IR spectra seem to trace the disk at 39 and 76 R-circle dot, respectively. We fit a power-law temperature distribution in the disk, finding an index of 0.8, comparable to optically thick accretion disk models.
Measuring Distance And Properties Of The Milky Way's Central Supermassive Black Hole With Stellar Orbits
(2008-12) Ghez, A. M.; Salim, S.; Weinberg, N. N.; Lu, J. R.; Do, T.; Dunn, J. K.; Matthews, K.; Morris, M. R.; Yelda, S.; Becklin, E. E.; Kremenek, T.; Milosavljevic, Milos; Naiman, J.; Naiman, J.
We report new precision measurements of the properties of our Galaxy's supermassive black hole. Based on astrometric (1995-2007) and radial velocity (RV; 2000-2007) measurements from the W. M. Keck 10m telescopes, a fully unconstrained Keplerian orbit for the short- period star S0- 2 provides values for the distance (R(0)) of 8.0 +/- 0.6 kpc, the enclosed mass (Mbh) of 4.1 +/- 0.6; 10(6) M(circle dot), and the black hole's RV, which is consistent with zero with 30 km s(-1) uncertainty. If the black hole is assumed to be at rest with respect to the Galaxy (e. g., has no massive companion to induce motion), we can further constrain the fit, obtaining R(0) = 8.4 +/- 0.4 kpc and M(bh) 4.5 +/- 0.4; 10(6) M(circle dot). More complex models constrain the extended dark mass distribution to be less than 3-4; 10(5) M(circle dot) within 0.01 pc, similar to 100 times higher than predictions from stellar and stellar remnant models. For all models, we identify transient astrometric shifts from source confusion (up to 5 times the astrometric error) and the assumptions regarding the black hole's radial motion as previously unrecognized limitations on orbital accuracy and the usefulness of fainter stars. Future astrometric and RV observations will remedy these effects. Our estimates of R(0) and the Galaxy's local rotation speed, which it is derived from combining R(0) with the apparent proper motion of Sgr A*, (theta(0) = 229 +/- 18 km s(-1)), are compatible with measurements made using other methods. The increased black hole mass found in this study, compared to that determined using projected mass estimators, implies a longer period for the innermost stable orbit, longer resonant relaxation timescales for stars in the vicinity of the black hole and a better agreement with the M(bh)-sigma relation.
A Multi-Site Campaign To Detect The Transit Of The Second Planet In Hat-P-13 (Research Note)
(2010) Szabo, G. M.; Kiss, L. L.; Benko, J. M.; Mezo, G.; Nuspl, J.; Regaly, Z.; Sarneczky, K.; Simon, A. E.; Leto, G.; Sanchez, R. Z.; Ngeow, C. C.; Kovari, Z.; Szabo, R.; Szabo, G. M.
Aims. A possible transit of HAT-P-13c had been predicted to occur on 2010 April 28. Here we report on the results of our multi-site campaign organised to detect the event. Methods. CCD photometric observations were carried out at five observatories in five countries. We reached 30% time coverage in a 5-day interval centered on the suspected transit of HAT-P-13c. Two transits of HAT-P-13b were also observed. Results. No transit of HAT-P-13c was detected during the campaign. By a numerical experiment with 10(5) model systems, we conclude that HAT-P-13c is not a transiting exoplanet with a significance level from 65% to 72%, depending on the planet parameters and the prior assumptions. We present two times of transit of HAT-P-13b ocurring at BJD 2 455 141.5522 +/- 0.0010 and BJD 2 455 249.4508 +/- 0.0020. The TTV of HAT-P-13b is consistent with zero within 0.001 days. The refined orbital period of HAT-P-13b is 2.916293 +/- 0.000010 days.
Precursors Prior To Type IIn Supernova Explosions Are Common: Precursor Rates, Properties, And Correlations
(2014-07) Ofek, Eran O.; Sullivan, Mark; Shaviv, Nir J.; Steinbok, Aviram; Arcavi, Iair; Gal-Yam, Avishay; Tal, David; Kulkarni, Shrinivas R.; Nugent, Peter E.; Ben-Ami, Sagi; Kasliwal, Mansi M.; Cenko, S. Bradley; Laher, Russ; Surace, Jason; Bloom, Joshua S.; Filippenko, Alexei V.; Silverman, Jeffrey M.; Yaron, Ofer; Silverman, Jeffrey M.
There is a growing number of Type IIn supernovae (SNe) which present an outburst prior to their presumably final explosion. These precursors may affect the SN display, and are likely related to poorly charted phenomena in the final stages of stellar evolution. By coadding Palomar Transient Factory (PTF) images taken prior to the explosion, here we present a search for precursors in a sample of 16 Type IIn SNe. We find five SNe IIn that likely have at least one possible precursor event (PTF 10bjb, SN 2010mc, PTF 10weh, SN 2011ht, and PTF 12cxj), three of which are reported here for the first time. For each SN we calculate the control time. We find that precursor events among SNe IIn are common: at the one-sided 99% confidence level, >50% of SNe IIn have at least one pre-explosion outburst that is brighter than 3 x 10(7) L-circle dot taking place up to 1/3 yr prior to the SN explosion. The average rate of such precursor events during the year prior to the SN explosion is likely greater than or similar to 1 yr(-1), and fainter precursors are possibly even more common. Ignoring the two weakest precursors in our sample, the precursors rate we find is still on the order of one per year. We also find possible correlations between the integrated luminosity of the precursor and the SN total radiated energy, peak luminosity, and rise time. These correlations are expected if the precursors are mass-ejection events, and the early-time light curve of these SNe is powered by interaction of the SN shock and ejecta with optically thick circumstellar material.
Searching For Dust Around Hyper Metal Poor Stars
(2014-08) Venn, Kim A.; Puzia, Thomas H.; Divell, Mike; Cote, Stephanie; Lambert, David L.; Starkenburg, Else; Lambert, David L.
We examine the mid-infrared fluxes and spectral energy distributions for stars with iron abundances [Fe/H] < -5, and other metal-poor stars, to eliminate the possibility that their low metallicities are related to the depletion of elements onto dust grains in the formation of a debris disk. Six out of seven stars examined here show no mid-IR excesses. These non-detections rule out many types of circumstellar disks, e. g., a warm debris disk (T <= 290 K), or debris disks with inner radii <= 1 AU, such as those associated with the chemically peculiar post-asymptotic giant branch spectroscopic binaries and RV Tau variables. However, we cannot rule out cooler debris disks, nor those with lower flux ratios to their host stars due to, e. g., a smaller disk mass, a larger inner disk radius, an absence of small grains, or even a multicomponent structure, as often found with the chemically peculiar Lambda Bootis stars. The only exception is HE0107-5240, for which a small mid-IR excess near 10 m is detected at the 2s level; if the excess is real and associated with this star, it may indicate the presence of (recent) dust-gas winnowing or a binary system.
Single Or Double Degenerate Progenitors? Searching For Shock Emission In The SDSS-II Type Ia Supernovae
(2010-10) Hayden, Brian T.; Garnavich, Peter M.; Kasen, Daniel; Dilday, Benjamin; Frieman, Joshua A.; Jha, Saurabh W.; Lampeitl, Hubert; Nichol, Robert C.; Sako, Masao; Schneider, Donald P.; Smith, Mathew; Sollerman, Jesper; Wheeler, J. Craig; Wheeler, J. Craig
From the set of nearly 500 spectroscopically confirmed Type Ia supernovae (SNe) and around 10,000 unconfirmed candidates from SDSS-II, we select a subset of 108 confirmed SNe Ia with well-observed early-time light curves to search for signatures from shock interaction of the SN with a companion star. No evidence for shock emission is seen; however, the cadence and photometric noise could hide a weak shock signal. We simulate shocked light curves using SN Ia templates and a simple Gaussian shock model to emulate the noise properties of the SDSS-II sample and estimate the detectability of the shock interaction signal as a function of shock amplitude, shock width, and shock fraction. We find no direct evidence for shock interaction in the rest-frame B-band, but place an upper limit on the shock amplitude at 9% of SN peak flux (M-B > -16.6 mag). If the single degenerate channel dominates type Ia progenitors, this result constrains the companion stars to be less than about 6 M-circle dot on the main sequence and strongly disfavors red giant companions.
A Spectropolarimetric View On The Nature Of The Peculiar Type I Sn 2005hk
(2010-10) Maund, Justyn R.; Wheeler, J. Craig; Wang, Lifan F.; Baade, Dietrich; Clocchiatti, Alejandro; Patat, Ferdinando; Hoflich, Patat; Quinn, Jason; Zelaya, Paula; Wheeler, J. Craig
We report two spectropolarimetric observations of SN 2005hk, which is a close copy of the "very peculiar" SN 2002cx, showing low peak luminosity, slow decline, high ionization near peak, and an unusually low expansion velocity of only about 7000 km s(-1). Further to the data presented by Chornock et al., at -4 days before maximum, we present data of this object taken on 2005 November 9 (near maximum) and November 23 (+ 2 weeks) that show the continuum and most of the spectral lines to be polarized at levels of about 0.2%-0.3%. At both epochs the data correspond to the Spectropolarimetric Type D1. The general low level of line polarization suggests that the line-forming regions for most species observed in the spectrum have a similar shape to that of the photosphere, which deviates from a spherical symmetry by <10%. In comparison with spectropolarimetry of Type Ia and core-collapse SNe at similar epochs, we find that the properties of SN 2005hk are most similar to those of Type Ia SNe. In particular, we find the low levels of continuum and line polarization to indicate that the explosion mechanism is approximately spherical, with homogeneous ejecta (unlike the chemically segregated ejecta of CCSNe). We discuss the possibility that SN 2005hk was the result of the pure deflagration of a white dwarf and note the issues concerning this interpretation.
The Spin-Orbit Alignment of the HD 17156 Transiting Eccentric Planetary System
(2008-08) Cochran, William D.; Redfield, Seth; Endl, Michael; Cochran, Anita L.; Cochran, William D.; Redfield, Seth; Endl, Michael; Cochran, Anita L.
We present high- precision radial velocity observations of HD 17156 during a transit of its eccentric Jovian planet. In these data, we detect the Rossiter- McLaughlin effect, which is an apparent perturbation in the velocity of the star due to the progressive occultation of part of the rotating stellar photosphere by the transiting planet. This system had previously been reported by Narita et al. in 2008 to exhibit a lambda = 62 degrees +/- 25 degrees misalignment of the projected planetary orbital axis and the stellar rotation axis. We model our data, along with the Narita et al. data, and obtain for the combined data set. We thus conclude that the planetary orbital axis is lambda = 9.4 degrees +/- 9.3 degrees for the combined data set. We thus conclude that the planetary orbital axis is actually very well aligned with the stellar rotation axis.
Testing Supernovae Ia Distance Measurement Methods With SN 2011fe
(2012-10) Vinko, J.; Sarneczky, K.; Takats, K.; Marion, G. H.; Hegedus, T.; Biro, I. B.; Borkovits, T.; Szegedi-Elek, E.; Farkas, A.; Klagyivik, P.; Kiss, L. L.; Kovacs, T.; Pal, A.; Szakats, R.; Szalai, N.; Szalai, T.; Szatmary, K.; Szing, A.; Vida, K.; Wheeler, J. C.; Vinko, J.
Aims. The nearby, bright, almost completely unreddened Type Ia supernova 2011fe in M101 provides a unique opportunity to test both the precision and the accuracy of the extragalactic distances derived from SNe Ia light curve fitters. Methods. We applied the current, public versions of the independent light curve fitting codes MLCS2k2 and SALT2 to compute the distance modulus of SN 2011fe from high-precision, multi-color (BVRI) light curves. Results. The results from the two fitting codes confirm that 2011fe is a >normal> (not peculiar) and only slightly reddened SN Ia. New unreddened distance moduli are derived as 29.21 +/- 0.07 mag (D similar to 6.95 +/- 0.23 Mpc, MLCS2k2), and 29.05 +/- 0.07 mag (6.46 +/- 0.21 Mpc). Conclusions. Despite the very good fitting quality achieved with both light curve fitters, the resulting distance moduli are inconsistent by 2 sigma. Both are marginally consistent (at similar to 1 sigma) with the Hubble Space Telescope key project distance modulus for M101. The SALT2 distance is in good agreement with the recently revised Cepheid- and TRGB-distance to M101. Averaging all SN- and Cepheid-based estimates, the absolute distance to M101 is similar to 6.6 +/- 0.5 Mpc.
The Very Young Type Ia Supernova 2012Cg: Discovery and Early-Time Follow-Up Observations
(2012-09) Silverman, Jeffrey M.; Ganeshalingam, Mohan; Cenko, S. Bradley; Filippenko, Alexei V.; Li, Weidong; Barth, Aaron J.; Carson, Daniel J.; Childress, Michael; Clubb, Kelsey I.; Cucchiara, Antonino; Graham, Melissa L.; Marion, G. H.; Nguyen, My L.; Pei, Liuyi; Tucker, Brad E.; Vinko, Jozsef; Wheeler, J. Craig; Worseck, Gabor; Vinko, Jozsef; Wheeler, J. Craig
On 2012 May 17.2 UT, only 1.5 +/- 0.2 days after explosion, we discovered SN 2012cg, a Type Ia supernova (SN Ia) in NGC 4424 (d approximate to 15 Mpc). As a result of the newly modified strategy employed by the Lick Observatory Supernova Search, a sequence of filtered images was obtained starting 161 s after discovery. Utilizing recent models describing the interaction of supernova (SN) ejecta with a companion star, we rule out a similar to 1 M-circle dot 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 similar to 17.3 days 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 greater than or similar to 14,000 km s(-1) at 2.5 days past explosion. Absorption from C II is detected early, as well as high-velocity components of both Si II lambda 6355 and Ca II. Our last spectrum (13.5 days 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.
What's Inside Black Holes
(The Texas Scientist, 2018) The Texas Scientist