Multi-band Light Curves Research Articles

FIRST-YEAR SPECTROSCOPY FOR THE SLOAN DIGITAL SKY SURVEY-II SUPERNOVA SURVEY

This paper presents spectroscopy of supernovae (SNe) discovered in the first season of the Sloan Digital Sky Survey-II SN Survey. This program searches for and measures multi-band light curves of SNe in the redshift range z = 0.05–0.4, complementing existing surveys at lower and higher redshifts. Our goal is to better characterize the SN population, with a particular focus on SNe Ia, improving their utility as cosmological distance indicators and as probes of dark energy. Our SN spectroscopy program features rapid-response observations using telescopes of a range of apertures, and provides confirmation of the SN and host-galaxy types as well as precise redshifts. We describe here the target identification and prioritization, data reduction, redshift measurement, and classification of 129 SNe Ia, 16 spectroscopically probable SNe Ia, 7 SNe Ib/c, and 11 SNe II from the first season. We also describe our efforts to measure and remove the substantial host-galaxy contamination existing in the majority of our SN spectra.

THE SLOAN DIGITAL SKY SURVEY-II SUPERNOVA SURVEY: SEARCH ALGORITHM AND FOLLOW-UP OBSERVATIONS

The Sloan Digital Sky Survey-II Supernova Survey has identified a large number of new transient sources in a 300 deg2 region along the celestial equator during its first two seasons of a three-season campaign. Multi-band (ugriz) light curves were measured for most of the sources, which include solar system objects, galactic variable stars, active galactic nuclei, supernovae (SNe), and other astronomical transients. The imaging survey is augmented by an extensive spectroscopic follow-up program to identify SNe, measure their redshifts, and study the physical conditions of the explosions and their environment through spectroscopic diagnostics. During the survey, light curves are rapidly evaluated to provide an initial photometric type of the SNe, and a selected sample of sources are targeted for spectroscopic observations. In the first two seasons, 476 sources were selected for spectroscopic observations, of which 403 were identified as SNe. For the type Ia SNe, the main driver for the survey, our photometric typing and targeting efficiency is 90%. Only 6% of the photometric SN Ia candidates were spectroscopically classified as non-SN Ia instead, and the remaining 4% resulted in low signal-to-noise, unclassified spectra. This paper describes the search algorithm and the software, and the real-time processing of the SDSS imaging data. We also present the details of the supernova candidate selection procedures and strategies for follow-up spectroscopic and imaging observations of the discovered sources.

Measuring type Ia supernova distances and redshifts from their multi-band light curves

The distance and redshift of a type Ia supernova can be determined simultaneously through its multi-band light curves. This fact may be used for imaging surveys that discover and obtain photometry for large numbers of supernovae; so many that it would be difficult to obtain a spectroscopic redshift for each. Using available supernova-analysis tools we find that there are several conditions in which a viable distance–redshift can be determined. Uncertainties in the effective distance at z∼0.3 are dominated by redshift uncertainties coupled with the steepness of the Hubble law. By z∼0.5 the Hubble law flattens out and distance modulus uncertainties dominate. Observations that give S/N=50 at peak brightness and a four-day observer cadence in each of griz-bands are necessary to match the intrinsic supernova magnitude dispersion out to z=1.0. Lower S/N can be tolerated with the addition of redshift priors (e.g. from a host-galaxy photometric redshift), observations in an additional redder band, or by focusing on supernova redshifts that have particular leverage for this measurement. More stringent S/N requirements are anticipated as improved systematics control over intrinsic color, metallicity, and dust is attempted to be drawn from light curves.

A spectroscopic study of the close eclipsing binary HS Herculis

Aims. New high-resolution spectroscopic observations of the eclipsing binary HS Herculis are presented. The main aims were to determine the stellar parameters of the two components, their evolutionary stage, and to search for spectroscopic evidence for a possible third body. Methods. Using the cross-correlation technique, we detect spectroscopically the faint secondary component of HS Herculis, and for the firts time measure its radial velocity. The primary and secondary radial velocity curves are analyzed simultaneously and the results of the orbital solution are combined with those derived from multiband light curve analysis to derive orbital and stellar parameters. Results. We find the masses to be M 1 = 4.49±0.16 and M 2 = 1.75±0.09 M ⊙ , the radii to be R 1 = 2.83±0.04 and R 2 = 1.61±0.02 R ⊙ , and the effective temperatures to be T 1 = 15 200 ± 750 K and T 2 = 7600 ± 400 K for the primary and secondary stars, respectively. We also derive projected rotational velocities of the components as υ 1 sin i = 81 ± 3 and υ 2 sin i = 24 ± 6. Conclusions. While a synchronous rotation for the primary star is indicated by the broadening of the spectral lines, the secondary component appears to rotate more slowly, nearly one half the synchronous rotation velocity. This discrepancy indicates that the less massive secondary component could have not yet attained tidal synchronization. Although the presence of a third body physically bound to the eclipsing pair has been suggested by many investigators, we find no sign of its presence in our CCD spectra. The evolutionary stage of the system's components is briefly discussed by comparing their physical parameters with those of theoretical models. We find that the two components are located near the zero-age main sequence, with an age of about 32 Myr.

Bayesian estimation applied to multiple species

Observed data are often contaminated by undiscovered interlopers, leading to biased parameter estimation. Here we present BEAMS (Bayesian estimation applied to multiple species) which significantly improves on the standard maximum likelihood approach in the case where the probability for each data point being “pure” is known. We discuss the application of BEAMS to future type-Ia supernovae (SNIa) surveys, such as LSST, which are projected to deliver over a million supernovae light curves without spectra. The multiband light curves for each candidate will provide a probability of being Ia (pure) but the full sample will be significantly contaminated with other types of supernovae and transients. Given a sample of N supernovae with mean probability, ⟨P⟩, of being Ia, BEAMS delivers parameter constraints equal to N⟨P⟩ spectroscopically confirmed SNIa. In addition BEAMS can be simultaneously used to tease apart different families of data and to recover properties of the underlying distributions of those families (e.g. the type-Ibc and II distributions). Hence BEAMS provides a unified classification and parameter estimation methodology which may be useful in a diverse range of problems such as photometric redshift estimation or, indeed, any parameter estimation problem where contamination is an issue.

Very Early Multicolor Observations of the Plateau Phase of the GRB 041006 Afterglow

Observations of the optical afterglow of GRB 041006 with the Kiso Observatory 1.05 m Schmidt telescope, the Lulin Observatory 1.0 m telescope and the Xinglong Observatory 0.6 m telescope. Three-bands (B, V and R) of photometric data points were obtained on 2004 October 6, 0.025-0.329 days after the burst. These very early multi band light curves imply the existence of a color dependent plateau phase. The B-band light curve shows a clear plateau at around 0.03 days after the burst. The R band light curve shows the hint of a plateau, or a possible slope change, at around 0.1 days after the burst. The overall behavior of these multi-band light curves may be interpreted in terms of the sum of two separate components, one showing a monotonic decay the other exhibiting a rising and a falling phase, as described by the standard afterglow model.

A Model-independent Photometric Redshift Estimator for Type Ia Supernovae

The use of Type Ia supernovae (SNe Ia) as cosmological standard candles is fundamental in modern observational cosmology. In this Letter, we derive a simple empirical photometric redshift estimator for SNe Ia using a training set of SNe Ia with multiband (griz) light curves and spectroscopic redshifts obtained by the Supernova Legacy Survey (SNLS). This estimator is analytical and model-independent; it does not use spectral templates. We use all the available SNe Ia from SNLS with near-maximum photometry in griz (a total of 40 SNe Ia) to train and test our photometric redshift estimator. The difference between the estimated redshifts zphot and the spectroscopic redshifts zspec, (zphot - zspec)/(1 + zspec), has rms dispersions of 0.031 for 20 SNe Ia used in the training set, and 0.050 for 20 SNe Ia not used in the training set. The dispersion is of the same order of magnitude as the flux uncertainties at peak brightness for the SNe Ia. There are no outliers. This photometric redshift estimator should significantly enhance the ability of observers to accurately target high-redshift SNe Ia for spectroscopy in ongoing surveys. It will also dramatically boost the cosmological impact of very large future supernova surveys, such as those planned for the Advanced Liquid-mirror Probe for Astrophysics, Cosmology, and Asteroids (ALPACA) and the Large Synoptic Survey Telescope (LSST).

The GRB 060218/SN 2006aj event in the context of other gamma-ray burst supernovae

The supernova SN 2006aj associated with GRB 060218 is the second-closest GRB-SN observed to date (z=0.033). We present Very Large Telescope, Liverpool Telescope, and Katzman Automatic Imaging Telescope multi-color photometry of SN 2006aj. This supernova is found to be subluminous and rapidly evolving. Its early light curve includes an additional wavelength-dependent component, which can be interpreted as shock break-out. We compare the photometric evolution of multi-band light curves with the corresponding properties of the present sample of more than 10 GRB-SNe with precisely known redshifts. Using host-galaxy extinction measurements, we derive extinction-corrected GRB-SN luminosities and place SN 2006aj in the context of this GRB-selected supernova sample as well as in the context of local stripped-envelope supernovae.

Testing dark energy with the Advanced Liquid-mirror Probe of Asteroids, Cosmology and Astrophysics

The Advanced Liquid-Mirror Probe of Asteroids, Cosmology and Astrophysics (ALPACA) is a proposed 8-meter liquid mirror telescope surveying 1000 square degree of the southern-hemisphere sky. It will be a remarkably simple and inexpensive telescope, that nonetheless will deliver a powerful sample of optical data for studying dark energy. The bulk of the cosmological data consists of nightly, high signal-to-noise, multiband light curves of SN Ia. At the end of the three-years run ALPACA is expected to collect 100,000 SNe Ia up to z~1. This will allow us to reduce present systematic uncertainties affecting the standard-candle relation. The survey will also provide several other datasets such as the detection of baryon acoustic oscillations in the matter power spectrum and shear weak lensing measurements. In this preliminary analysis we forecast constraints on dark energy parameters from SN Ia and baryon acoustic oscillations. The combination of these two datasets will provide competitive constraints on the dark energy parameters under minimal prior assumptions. Further studies are needed to address the accuracy of weak lensing measurements.

Accretion mode changes in Centaurus X-3

We report here discovery of the existence of two different accretion modes in the high mass X-ray bin binary pulsar Cen X-3 during its high states binary The multiband X-ray light curves of Cen X-3 lasting for more than 3400 days obtained with the All Sky Monitor (ASM) on board the Rossi X-ray Timing Explorer (RXTE) shows many episodes of high and low X-ray intensities. The high intensity phases last between a few to upto 110 days and the separation between two high intensity phases also varies widely. One remarkable feature deduced from the RXTE-ASM light curves is that during these high intensity phases, Cen X-3 manifests in two very distinct spectral states. When the source makes a transitionf rom the low intensity phase to the high intensity phase, it adopts one of these two spectral states and during the entire high intensity phase remains in that particular spectral state. During December 2000 to April 2004, all the high intensity episodes showed a hardness ratio which is significantly larger than the same during all the high states prior to and subsequent to this period. It is also found that most of the soft outbursts reach a nearly constant peak flux in the 5-12 ke Vband. For comparison, similar analysis was carried out on the long term X-ray light curves of three other X-ray binary pulsars Her X-1, Vela X-1, and SMC X-1. Results obtained with these sources are also presented here and we found that none of the other sources show such a behaviour. From these observations, we suggest that Cen X-3 has two different accretion modes and in the course of nine years it has exhibited two switch overs between these.

Multiband optical photometry and bolometric light curve of the Type Ia supernova 2004S

We present BVRCIC broad-band CCD photometry of the Type Ia supernova SN 2004S, which appeared in the galaxy MCG–05-16-021, obtained during 2004 February 12 to March 22. We present multiband and bolometric light curves constructed using our data as well as other available data. The time of the B-band maximum and the peak magnitudes in different bands are obtained using fits of light-curve and colour templates. We clearly see a strong shoulder in the RC band and a second maximum in the IC band. SN 2004S closely resembles SN 1992al after maximum. From the peak bolometric luminosity, we estimate the ejected mass of 56 Ni to be 0.41 M⊙.

A "Pulsational" Distance Determination for the Large Magellanic Cloud

We present results from the theoretical modelling of the observed B,V light curves of 14 RR Lyrae stars in the Large Magellanic Cloud. The sample includes 7 fundamental and 7 first overtone pulsators covering the metallicity range from -2.12 to -0.79 dex in [Fe/H], with average value of -1.54 dex. Masses, intrinsic luminosities, effective temperatures, and reddenings were derived by fitting high accuracy multiband light curves available for these RR Lyrae stars to nonlinear convective pulsation models. Individual distance moduli were determined for each variable, they lead to an average distance modulus for the Large Magellanic Cloud of (m-M)o= 18.54 +/-0.02 (sigm= 0.09 mag, standard deviation of the average), in good agreement with the long astronomical distance scale.

Discovery of Two Distant Type Ia Supernovae in the Hubble Deep Field–North with the Advanced Camera for Surveys

We present observations of the rst two supernovae discovered with the recently installed Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST). The supernovae were found in Wide Field Camera images of the Hubble Deep Field North taken with the F775W, F850LP, and G800L optical elements as part of the ACS guaranteed time observation program. Spectra extracted from the ACS G800L grism exposures conrm that the objects are Type Ia supernovae (SNe Ia) at redshifts z = 0 47 and z = 0 95. Follow-up HST observations have been conducted with ACS in F775W and F850LP and with NICMOS in the near-infrared F110W bandpass, yielding a total of 9 ux measurements in the 3 bandpasses over a period of 50 days in the observed frame. We discuss many of the important issues in doing accurate photometry with the ACS. We analyze the multi-band light curves using two different tting methods to calibrate the supernovae luminosities and place them on the SNe Ia Hubble diagram. The resulting distances are consistent with the redshift-distance relation of the accelerating universe model, although evolving intergalactic grey dust remains as a less likely possibility. The relative ease with which these SNe Ia were found, conrmed, and monitored demonstrates the potential ACS holds for revolutionizing the eld of high-redshift SNe Ia, and therefore of testing the accelerating universe cosmology and constraining the iepoch of deceleration.i Subject headings: cosmology: observations o supernovae: general o supernovae: individual (SN 2002dc, SN 2002dd)

UBVRI CCD Observations and Analyses for the Near-Contact Binary, LP Cephei

view Abstract Citations (2) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS UBVRI CCD Observations and Analyses for the Near-Contact Binary, LP Cephei Samec, Ronald G. ; McDermith, Richard J. ; Carrigan, Brian J. ; Gray, Jamison D. Abstract As part of our study of eccentric eclipsing binary candidates, we have obtained multiband CCD light curves of LP Cephei formed from observations taken at Kitt Peak National Observatory in 1994 September. The CCDPHOT system was used in conjunction with the 0.9 m Cassegrain reflector telescope and standard Johnson U, B, V, and Cousins R and I filters. Five epochs of minimum light were determined and an improved linear ephemeris was calculated. The first published synthetic light curve solutions of LP Cep are presented. Our analysis reveals that LP Cep is in a near-contact semidetached configuration consisting of an F2 spectral-type primary component with a fillout ∼78% and a K1 secondary filling its Roche lobe. Despite the earlier reports that LP Cep has a displaced secondary eclipse, our light curves show no such effect. The presence of a spot due to a tenuous, intermittent gas stream and star spot activity may be the source of such asymmetries. Publication: The Astronomical Journal Pub Date: February 1997 DOI: 10.1086/118301 Bibcode: 1997AJ....113..800S Keywords: STARS: INDIVIDUAL: LP CEPHEI; BINARIES: ECLIPSING full text sources ADS | data products SIMBAD (1)

Delayed detonation models for normal and subluminous type IA sueprnovae: Absolute brightness, light curves, and molecule formation

We compute optical and infrared light curves of the pulsating class of delayed detonation models for Type Ia supernovae (SN Ia's) using an elaborate treatment of the Local Thermodynamic Equilbrium (LTE) radiation transport, equation of state and ionization balance, expansion opacity including the cooling by CO, Co(+), and SiO, and a Monte Carlo gamma-ray deposition scheme. The models have an amount of Ni-56 in the range from approximately or equal to 0.1 solar mass up to 0.7 solar mass depending on the density at which the transition from a deflagration to a detonation occurs. Models with a large nickel production give light curves comparable to those of typical Type Ia supernovae. Subluminous supernovae can be explained by models with a low nickel production. Multiband light curves are presented in comparison with the normally bright event SN 1992bc and the subluminous events Sn 1991bg and SN 1992bo to establish the principle that the delayed detonation paradigm in Chandrasekhar mass models may give a common explosion mechanism accounting for both normal and subluminous SN Ia's. Secondary IR-maxima are formed in the models of normal SN Ia's as a photospheric effect if the photospheric radius continues to increase well after maximum light. Secondary maxima appear later and stronger in models with moderate expansion velocities and with radioactive material closer to the surface. Model light curves for subluminous SN Ia's tend to show only one 'late' IR-maximum. In some delayed detonation models shell-like envelopes form, which consist of unburned carbon and oxygen. The formation of molecules in these envelopes is addressed. If the model retains a C/O-envelope and is subluminous, strong vibration bands of CO may appear, typically several weeks past maximum light. CO should be very weak or absent in normal Sn Ia's.