Light curves

This paper seeks to use data from Colgate University’s Foggy Bottom Observatory to confirm an established relationship between the peak luminosities and light curve shapes of type Ia supernovae. Using this relationship, and the peak apparent brightnesses observed at Foggy Bottom Observatory, the distance to SN 1991M in the galaxy IC 1151 will be determined. The process used will be evaluated for success, and will set the standard for future supernova photometry at Colgate.

Algorithms for drawing smooth curves and surfaces are well-known but may be too expensive in CPU time to use for certain high speed interactive graphics applications. This paper looks at some new geometrically-based smoothing algorithms that arrive at the final smooth curve or surface after the application of an infinite number of iterations of the algorithm using subdivision refinement. When CPU time is scarce low iteration counts can be used to provide an acceptable level of approximation of smoothness and when CPU time is more plentiful higher levels of iteration can be applied for greater visual smoothing accuracy. Three new algorithms are presented and analysed. Convergence is proved geometrically for each and their timings are reported. Mixing iterations provides new opportunities for achieving various different effects in curve and surface smoothing.

The investigation of space debris involves the characterization of orbital objects, which includes the collection of information like orbit, body shape and attitude. Current studies are mainly concerned with methods for precise orbit determination. However, future removal missions will need additional information of the objects state – in particular the attitude. For this purpose, researchers of the Institute of Technical Physics at the German Aerospace Center (DLR) in Stuttgart, Germany started a new research campaign to investigate light curves of debris objects.

We present spectroscopic and photometric results of Nova V1280 Sco which was discovered in outburst in early 2007 February. The large number of spectra obtained of the object leads to one of the most extensive, near-infrared spectral studies of a classical nova. The spectra evolve from a P-Cygni phase to an emission-line phase and at a later stage is dominated by emission from the dust that formed in this nova. A detailed model is computed to identify and study characteristics of the spectral lines. Inferences from the model address the vexing question of which novae have the ability to form dust. It is demonstrated, and strikingly corroborated with observations, that the presence of lines in the early spectra of low-ionization species like Na and Mg - indicative of low temperature conditions - appear to be reliable indicators that dust will form in the ejecta. It is theoretically expected that mass loss during a nova outburst is a sustained process. Spectroscopic evidence for such a sustained mass loss, obtained by tracing the evolution of a P-Cygni feature in the Brackett gamma line, is presented here allowing a lower limit of 25-27 days to be set for the mass-loss duration. Photometric data recording the nova's extended 12 day climb to peak brightness after discovery is used to establish an early fireball expansion and also show that the ejection began well before maximum brightness. The JHK light curves indicate the nova had a fairly strong second outburst around 100 days after the first.

We present I and B photometry of five distinct transits of the exoplanet OGLE-TR-10b. By modeling the light curves, we find the planetary radius to be RP=(1.06+/-0.08)RJup and the stellar radius to be RS=1.10+/-0.07 Rsolar. The uncertainties are dominated by statistical errors in the photometry. Our estimate of the planetary radius is smaller than previous estimates that were based on lower precision photometry, and hence the planet is not as anomalously large as was previously thought. We provide updated determinations of all the system parameters, including the transit ephemerides.

Symbiotic stars are long-orbital-period interacting binaries characterized by extended emission over the whole electromagnetic range and by complex photometric and spectroscopic variability. In this paper, the first of a series, we present Optical Gravitational Lensing Experiment (OGLE) light curves of all the confirmed symbiotic stars in the Large Magellanic Cloud, with one exception. By careful visual inspection and combined time series analysis techniques, we investigate for the first time in a systematic way the photometric properties of these astrophysical objects, trying in particular to distinguish the nature of the cool component (e.g. semiregular Variable versus OGLE small-amplitude red giant), to provide its first-order pulsational ephemerides and to link all this information with the physical parameters of the binary system as a whole. Among the most interesting results, there is the discovery of a 20 yr-long steady fading of Sanduleak's star, a peculiar symbiotic star known to produce the largest stellar jet ever discovered. We discuss by means of direct examples the crucial need for long-term multi-band observations to get a real understanding of symbiotic and other interacting binary stars. We eventually introduce BOMBOLO, a multi-band simultaneous imager for the Southern Astrophysical Research 4 m Telescope, whose design and construction we are currently leading.

The precise derivation of transit depths from transit light curves is a key component for measuring exoplanet transit spectra, and henceforth for the study of exoplanet atmospheres. However, it is still deeply affected by various kinds of systematic errors and noise. In this paper we propose a new detrending method by reconstructing the stellar flux baseline during transit time. We train a probabilistic Long Short-Term Memory (LSTM) network to predict the next data point of the light curve during the out-of-transit, and use this model to reconstruct a transit-free light curve-i.e. including only the systematics-during the in-transit. By making no assumption about the instrument, and using only the transit ephemeris, this provides a general way to correct the systematics and perform a subsequent transit fit. The name of the proposed model is TLCD-LSTM, standing for Transit Light Curve Detrending LSTM. Here we present the first results on data from six transit observations of HD 189733 b with the IRAC camera on board the Spitzer Space Telescope, and discuss some of its possible further applications.

ABSTRACT We confirm our earlier tentative detection of M31* in X-rays and measure its light curve and spectrum. Observations in 2004-2005 find M31* rather quiescent in the X-ray and radio. However, X-ray observations in 2006-2007 show M31* to be highly variable at times. A separate variable X-ray source is found near P1, the brighter of the two optical nuclei. The apparent angular Bondi radius of M31* is the largest of any black hole and large enough to be well resolved with Chandra. The diffuse emission within this Bondi radius is found to have an X-ray temperature ~0.3 keV and density 0.1 cm–3, indistinguishable from the hot gas in the surrounding regions of the bulge given the statistics allowed by the current observations. The X-ray source at the location of M31* is consistent with a point source and a power-law spectrum with energy slope 0.9 ± 0.2. Our identification of this X-ray source with M31* is based solely on positional coincidence.

We present X-ray, broad band optical and low frequency radio observations of the bright type IIP supernova SN 2004et. The \cxo observed the supernova at three epochs, and the optical coverage spans a period of $\sim$ 470 days since explosion. The X-ray emission softens with time, and we characterise the X-ray luminosity evolution as $\Lx \propto t^{-0.4}$. We use the observed X-ray luminosity to estimate a mass-loss rate for the progenitor star of $\sim \ee{2}{-6} M_\odot \mathrm{yr}^{-1}$. The optical light curve shows a pronounced plateau lasting for about 110 days. Temporal evolution of photospheric radius and color temperature during the plateau phase is determined by making black body fits. We estimate the ejected mass of $^{56}$Ni to be 0.06 $\pm$ 0.03 M$_\odot$. Using the expressions of Litvinova & Nad\"{e}zhin (1985) we estimate an explosion energy of (0.98 $\pm$ 0.25) $\times 10^{51}$ erg. We also present a single epoch radio observation of SN 2004et. We compare this with the predictions of the model proposed by Chevalier et al. (2006). These multi-wavelength studies suggest a main sequence progenitor mass of $\sim$ 20 M$_\odot$ for SN 2004et.

In recent work we suggested that photons of energy >100 MeV detected from GRBs by the Fermi Satellite are produced via synchrotron emission in the external forward shock with a weak magnetic field - consistent with shock compressed upstream magnetic field of a few tens of micro-Gauss. Here we investigate whether electrons can be accelerated to energies such that they radiate synchrotron photons with energy up to about 10 GeV in this particular scenario. We do this using two methods: (i) we check if these electrons can be confined to the shock front; and (ii) we calculate radiative losses while they are being accelerated. We find that these electrons remain confined to the shock front, as long as the upstream magnetic field is >~ 10 micro-Gauss, and don't suffer substantial radiative losses, the only condition required is that the external reverse shock emission be not too bright: peak flux less than 1 Jy in order to produce photons of 100 MeV, and less than ~100 mJy for producing 1-GeV photons. We also find that the acceleration time for electrons radiating at 100 MeV is a few seconds (in observer frame), and the acceleration time is somewhat longer for electrons radiating at a few GeV. This could explain the lack of >100 MeV photons for the first few seconds after the trigger time for long GRBs reported by the Fermi Satellite, and also the slight lag between photons of GeV and 100 MeV energies. We model the onset of the external forward shock light curve in this scenario and find it consistent with the sharp rise observed in the 100-MeV light curve of GRB080916C and similar bursts.

We combine the CfA3 supernova Type Ia (SN Ia) sample with samples from the literature to calculate improved constraints on the dark energy equation of state parameter, w. The CfA3 sample is added to the Union set of Kowalski et al. (2008) to form the Constitution set and, combined with a BAO prior, produces 1+w=0.013 +0.066/-0.068 (0.11 syst), consistent with the cosmological constant. The CfA3 addition makes the cosmologically-useful sample of nearby SN Ia between 2.6 and 2.9 times larger than before, reducing the statistical uncertainty to the point where systematics play the largest role. We use four light curve fitters to test for systematic differences: SALT, SALT2, MLCS2k2 (R_V=3.1), and MLCS2k2 (R_V=1.7). SALT produces high-redshift Hubble residuals with systematic trends versus color and larger scatter than MLCS2k2. MLCS2k2 overestimates the intrinsic luminosity of SN Ia with 0.7 < Delta < 1.2. MLCS2k2 with R_V=3.1 overestimates host-galaxy extinction while R_V=1.7 does not. Our investigation is consistent with no Hubble bubble. We also find that, after light-curve correction, SN Ia in Scd/Sd/Irr hosts are intrinsically fainter than those in E/S0 hosts by 2 sigma, suggesting that they may come from different populations. We also find that SN Ia in Scd/Sd/Irr hosts have low scatter (0.1 mag) and reddening. Current systematic errors can be reduced by improving SN Ia photometric accuracy, by including the CfA3 sample to retrain light-curve fitters, by combining optical SN Ia photometry with near-infrared photometry to understand host-galaxy extinction, and by determining if different environments give rise to different intrinsic SN Ia luminosity after correction for light-curve shape and color.

We present a de-trending algorithm for the removal of trends in time series. Trends in time series could be caused by various systematic and random noise sources such as cloud passages, changes of airmass, telescope vibration or CCD noise. Those trends undermine the intrinsic signals of stars and should be removed. We determine the trends from subsets of stars that are highly correlated among themselves. These subsets are selected based on a hierarchical tree clustering algorithm. A bottom-up merging algorithm based on the departure from normal distribution in the correlation is developed to identify subsets, which we call clusters. After identification of clusters, we determine a trend per cluster by weighted sum of normalized light-curves. We then use quadratic programming to de-trend all individual light-curves based on these determined trends. Experimental results with synthetic light-curves containing artificial trends and events are presented. Results from other de-trending me...