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Register a new userUsing the Palomar Transient Factory to Search for Ultra-Long-Period Cepheid Candidates in M31
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Ultra-long-period Cepheids (ULPCs) are important in distance-scale studies due to their potential for determining distance beyond ~100 Mpc. We performed a comprehensive search for ULPCs in M31, a local benchmark to calibrate the distance ladders. We use data from the Palomar Transient Factory (PTF), which has imaged M31 using a 1.2-m telescope equipped with a ~7.26 deg2 field-of-view (FOV) camera, usually with daily sampling, since the beginning of 2010. The large FOV, together with the regular monitoring, enables us to probe ULPCs in the bulge, disk, and even out to the halo of M31. Using a difference imaging analysis technique, we found and characterized 3 promising ULPC candidates based on their luminosities, amplitudes and Fourier parameters. The mean absolute magnitude for these 3 ULPC candidates, calibrated with latest M31 distance, is M_R=-6.47mag. Two out of the 3 ULPC candidates have been reported in literature, however their published periods from Magnier et al. are about half of the periods we found in this work. The third ULPC candidate is a new discovery. We studied 5 other candidates and determined that they are probably Mira-like or ultra-long-period variables, but not ULPCs.
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The ultra-long period Cepheids (ULPCs) are classical Cepheids with pulsation periods exceeding $approx 80$ days. The intrinsic brightness of ULPCs are ~1 to ~3 mag brighter than their shorter period counterparts. This makes them attractive in future distance scale work to derive distances beyond the limit set by the shorter period Cepheids. We have initiated a program to search for ULPCs in M31, using the single-band data taken from the Palomar Transient Factory, and identified eight possible candidates. In this work, we presented the VI-band follow-up observations of these eight candidates. Based on our VI-band light curves of these candidates and their locations in the color-magnitude diagram and the Period-Wesenheit diagram, we verify two candidates as being truly ULPCs. The six other candidates are most likely other kinds of long-period variables. With the two confirmed M31 ULPCs, we tested the applicability of ULPCs in distance scale work by deriving the distance modulus of M31. It was found to be $mu_{M31,ULPC}=24.30pm0.76$ mag. The large error in the derived distance modulus, together with the large intrinsic dispersion of the Period-Wesenheit (PW) relation and the small number of ULPCs in a given host galaxy, means that the question of the suitability of ULPCs as standard candles is still open. Further work is needed to enlarge the sample of calibrating ULPCs and reduce the intrinsic dispersion of the PW relation before re-considering ULPCs as suitable distance indicators.
Using data from the (intermediate) Palomar Transient Factory (iPTF), we characterize the time variability of ~500 massive stars in M31. Our sample is those stars which are spectrally typed by Massey and collaborators, including Luminous Blue Variables, Wolf-Rayets, and warm and cool supergiants. We use the high-cadence, long-baseline (~5 years) data from the iPTF survey, coupled with data-processing tools that model complex features in the light curves. We find widespread photometric (R-band) variability in the upper Hertzsprung Russell diagram (or CMD) with an increasing prevalence of variability with later spectral types. Red stars (V-I>1.5) exhibit larger amplitude fluctuations than their bluer counterparts. We extract a characteristic variability timescale, tch, via wavelet transformations that are sensitive to both continuous and localized fluctuations. Cool supergiants are characterized by longer timescales (>100 days) than the hotter stars. The latter have typical timescales of tens of days but cover a wider range, from our resolution limit of a few days to longer than 100 days timescales. Using a 60-night block of data straddling two nights with a cadence of around 2 minutes, we extracted tch in the range 0.1--10 days with amplitudes of a few percent for 13 stars. Though there is broad agreement between the observed variability characteristics in the different parts of the upper CMD with theoretical predictions, detailed comparison requires models with a more comprehensive treatment of the various physical processes operating in these stars such as pulsation, subsurface convection, and the effect of binary companions.
The Palomar Transient Factory proves to be a prolific source of Magnetic Cataclysmic Variables, selected by their distinctive photometric variability, and followed up spectroscopically. Here, we present six new candidate systems, together with preliminary photometric periods and spectra.
We present results of the Sky2Night project: a systematic, unbiased search for fast optical transients with the Palomar Transient Factory. We have observed 407 deg$^2$ in $R$-band for 8 nights at a cadence of 2 hours. During the entire duration of the project, the 4.2m William Herschel Telescope on La Palma was dedicated to obtaining identification spectra for the detected transients. During the search, we found 12 supernovae, 10 outbursting cataclysmic variables, 9 flaring M-stars, 3 flaring active Galactic nuclei and no extragalactic fast optical transients. Using this systematic survey for transients, we have calculated robust observed rates for the detected types of transients, and upper limits of the rate of extragalactic fast optical transients of $mathcal{R}<37times 10^{-4}$deg$^{-2}$d$^{-1}$ and $mathcal{R}<9.3times 10^{-4}$deg$^{-2}$d$^{-1}$ for timescales of 4h and 1d and a limiting magnitude of $Rapprox19.7$. We use the results of this project to determine what kind of and how many astrophysical false positives we can expect when following up gravitational wave detections in search for kilonovae.
Type Ic supernovae represent the explosions of the most stripped massive stars, but their progenitors and explosion mechanisms remain unclear. Larger samples of observed supernovae can help characterize the population of these transients. We present an analysis of 44 spectroscopically normal Type Ic supernovae, with focus on the light curves. The photometric data were obtained over 7 years with the Palomar Transient Factory (PTF) and its continuation, the intermediate Palomar Transient Factory (iPTF). This is the first homogeneous and large sample of SNe Ic from an untargeted survey, and we aim to estimate explosion parameters for the sample. We present K-corrected Bgriz light curves of these SNe, obtained through photometry on template-subtracted images. We performed an analysis on the shape of the $r$-band light curves and confirmed the correlation between the rise parameter Delta m_{-10} and the decline parameter Delta m_{15}. Peak r-band absolute magnitudes have an average of -17.71 +- 0.85 mag. To derive the explosion epochs, we fit the r-band lightcurves to a template derived from a well-sampled light curve. We computed the bolometric light curves using r and g band data, g-r colors and bolometric corrections. Bolometric light curves and Fe II lambda 5169 velocities at peak were used to fit to the Arnett semianalytic model in order to estimate the ejecta mass M_{ej}, the explosion energy E_{K} and the mass of radioactive nickel (M(56) Ni) for each SN. Including 41 SNe, we find average values of <M_{ej}>=4.50 +-0.79 msun, <E_{K}>=1.79 +- 0.29 x10^{51} erg, and <M(56)Ni)>= 0.19 +- 0.03 msun. The explosion-parameter distributions are comparable to those available in the literature, but our large sample also includes some transients with narrow and very broad light curves leading to more extreme ejecta masses values.
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