Publications of the Astronomical Society of the Pacific

Li, Weidong; Van Dyk, Schuyler D.; Filippenko, Alexei V.; Cuillandre, Jean‐Charles

doi: 10.1086/428278pmid: N/A

Supernova (SN) 2004et is the eighth historical SN in the nearby spiral galaxy NGC 6946. Here we report on early photometric and spectroscopic monitoring of this object. SN 2004et is a Type II event, exhibiting a plateau in its light curves, but its spectral and color evolution appear to differ significantly from those of other, more normal Type II plateau (II‐P) SNe. We have analyzed Canada‐France‐Hawaii Telescope images of the host galaxy taken prior to the SN explosion, identifying a candidate progenitor for the SN. The star’s absolute magnitude and intrinsic color imply that it was a yellow, rather than red, supergiant star, with an estimated zero‐age main‐sequence mass of 15+5-2 M⊙. Although this mass estimate is consistent with estimates and upper limits for the progenitors of other, more normal SNe II‐P, the SN 2004et progenitor’s unusual color could further imply a preexplosion evolutionary history analogous to, but less extreme than, that for the progenitors of the peculiar Type II‐P SN 1987A or the Type IIb SN 1993J. The identity of the progenitor candidate needs to be verified when the SN has significantly dimmed.

Rajala, Anne M.; Fox, Derek B.; Gal‐Yam, Avishay; Leonard, Douglas C.; Soderberg, Alicia M.; Kulkarni, S. R.; Cenko, S. Bradley; Moon, Dae‐Sik; Harrison, Fiona A.

doi: 10.1086/427985pmid: N/A

We present photometric typing analyses of three young supernovae observed with the robotic 60 inch (1.5 m) telescope at Palomar Observatory (P60). This represents the first time that such phototyping, conducted in a blind fashion, has been attempted on newly discovered supernovae. For one of the target supernovae, SN 2004cs, our photometry provided the first constraint on the supernova type, which we predicted would be Type Ia. Contrary to expectations, however, our subsequent Keck spectroscopy shows it to be an unusual Type II supernova. For each of the other two supernovae (SN 2004dh [Type II] and SN 2004dk [Type Ib]), our phototyping results are consistent with the known event type as determined from ground‐based spectroscopy. However, the colors of SN 2004dk are also consistent with a Type Ic or Type II classification. We discuss our approach to the challenges of phototyping—contamination by host galaxy light and the unknown photometric quality of the data—for cases in which it is desirable to complete the analysis with just one night of observations. The growing interest in the properties and behavior of very young supernovae, and the increased discovery rate for such events, mean that prompt phototyping analyses can provide useful input for observational campaigns. Our results demonstrate the value and feasibility of such a project for P60, at the same time illustrating its chief inherent shortcoming: an inability to identify new and unusual events as such without later spectroscopic observations.

von Braun, Kaspar; Lee, Brian L.; Seager, S.; Yee, H. K. C.; Mallén‐Ornelas, Gabriela; Gladders, Michael D.

doi: 10.1086/427982pmid: N/A

Open clusters potentially provide an ideal environment for the search for transiting extrasolar planets, since they feature a relatively large number of stars of the same known age and metallicity at the same distance. With this motivation, over a dozen open clusters are now being monitored by four different groups. We review the motivations and challenges for open cluster transit surveys for short‐period giant planets. Our photometric monitoring survey of Galactic southern open clusters, the Extrasolar Planet Occultation Research/Open Clusters (EXPLORE/OC) project, was designed with the goals of maximizing the chance of finding and characterizing planets and of providing a statistically valuable astrophysical result in the case of no detections. We use the EXPLORE/OC data from two open clusters, NGC 2660 and NGC 6208, to illustrate some of the largely unrecognized issues facing open cluster surveys, including severe contamination by Galactic field stars (>80%) and the relatively low number of cluster members for which high‐precision photometry can be obtained. We discuss how a careful selection of open cluster targets under a wide range of criteria such as cluster richness, observability, distance, and age can meet the challenges, maximizing chances to detect planet transits. In addition, we present the EXPLORE/OC observing strategy to optimize planet detection, which includes high‐cadence observing and continuously observing individual clusters rather than alternating between targets.

Guis, V.; Barge, P.

doi: 10.1086/427984pmid: N/A

A new method is proposed for signal denoising and transit detection in stellar photometric light curves. The plane of a light curve can be considered as a two‐dimensional image that splits into two parts: the upper and lower part of the plot itself. The two resulting images are then analyzed with an image‐processing method that enables us to develop new algorithms for filtering and detection. The resulting denoising algorithm is more efficient than standard filters, such as the convolution filter, and can be applied recursively without changing the signals of interest. The new detection algorithm has a performance similar to that of the matched filter, but also exhibits greater “sensitivity” at a given confidence level. These new filtering and detection algorithms can operate on selected parts of a light curve, which is important for processing data flows or analyzing interrupted data sequences. They have been developed and tested on simulated light curves created using a physical model of the COROT (Convection, Rotation, and Planetary Transits) instrument being developed for the mission. The algorithms provide interesting perspectives on how the detection of weak transit events might be improved.

Pinfield, D. J.; Jones, H. R. A.; Steele, I. A.

doi: 10.1086/427983pmid: N/A

We present the results of a simulation to investigate the prospects of measuring mass, age, radius, metallicity, and luminosity data for brown dwarfs in fully eclipsing binary systems around dwarf spectral types from late K to early M that could be identified by ultra–wide‐field transit surveys such as SuperWASP. These surveys will monitor approximately a million K and M dwarfs with |b|>20° (where blending of sources is not a significant problem) at a level sufficient to detect transits of low‐luminosity companions. We look at the current observational evidence for such systems and suggest that ∼1% of late K and early‐to‐mid M dwarfs could have a very close (∼0.02 AU) brown dwarf companion. With this assumption, and using SuperWASP as an example, our simulation predicts that ∼400 brown dwarfs in fully eclipsing binary systems could be discovered. All of these eclipsing binaries could yield accurate brown dwarf mass and radius measurements from radial velocity and follow‐up light curve measurements. By inferring the brown dwarf effective temperature distribution, assuming a uniform age spread and an α = 0.5 companion brown dwarf mass function, the simulation estimates that brown dwarf brightness could also be measurable (at the 10% level) for ∼60 of these binary systems from near‐infrared follow‐up light curves of the secondary eclipse. We consider irradiation of these brown dwarfs by their primary stars and conclude that it would be below the 10% level for ∼70% of them. This means that in these cases, the measured brown dwarf brightnesses should essentially be the same as those of free‐floating counterparts. The predicted age distribution of the primaries is dominated by young systems, and ∼20 binaries could be younger than 1 Gyr. Irradiation will be below the 10% level for ∼80% of these. We suggest that many of these young binary systems will be members of “kinematic moving groups,” allowing their ages to be accurately constrained.

Espaillat, Catherine; Patterson, Joseph; Warner, Brian; Woudt, Patrick

doi: 10.1086/427959pmid: N/A

We report photometry of the helium‐rich cataclysmic variable ES Ceti during 2001–2004. The star is roughly stable at V∼17.0 and has a light curve dominated by a single period of 620 s, which remains measurably constant over the 3 yr baseline. The weight of evidence suggests that this is the true orbital period of the underlying binary, not a “superhump” as initially assumed. We report GALEX ultraviolet magnitudes that establish a very blue flux distribution (Fν∼ν1.3) and therefore a large bolometric correction. Other evidence (the very strong He ii λ4686 emission and a ROSAT detection in soft X‐rays) also indicates a strong EUV source, and comparison to helium atmosphere models suggests a temperature of 130 ± 10 kK. For a distance of 350 pc, we estimate a luminosity of (0.8–1.7) × 1034 ergs s−1, yielding a mass accretion rate of (2–4) × 10-9 M⊙ yr−1 onto an assumed 0.7 M⊙ white dwarf. This appears to be about as expected for white dwarfs orbiting each other in a 10 minute binary, assuming that mass transfer is powered by gravitational radiation losses. We estimate mean accretion rates for other helium‐rich cataclysmic variables and find that they also follow the expected M˙∼P-5o relation. There is some evidence (the lack of superhumps and the small apparent size of the luminous region) that the mass‐transfer stream in ES Cet directly strikes the white dwarf, rather than circularizing to form an accretion disk.

Le Bertre, T.; Tanaka, M.; Yamamura, I.; Murakami, H.; MacConnell, D. J.

doi: 10.1086/427986pmid: N/A

We have identified 139 cool carbon stars in the near‐infrared spectrophotometric survey of the Infrared Telescope in Space (IRTS) from the conspicuous presence of molecular absorption bands at 1.8, 3.1, and 3.8 μm. Among them, 14 are new bright (K∼4.0–7.0) carbon stars. We find a trend relating the 3.1 μm band strength to the K - L′ color index, which is known to correlate with mass‐loss rate. This could be an effect of a relation between the depth of the 3.1 μm feature and the degree of development of the extended stellar atmosphere where dust starts to form.

Turner, David G.; Savoy, Jonathan; Derrah, Jayme; Abdel‐Sabour Abdel‐Latif, Mohamed; Berdnikov, Leonid N.

doi: 10.1086/427838pmid: N/A

The evolutionary changes in pulsation period for the Cepheid Polaris are reinvestigated using archival observational material (radial velocities, photometry, and eye observations) over the interval 1844 to the present, including new photometry for the star obtained in 2003–2004. The star’s pulsation period increased at a rate of 4.5 s yr−1 during that interval, with the exception of a brief hiatus between 1963 and 1966, when it suddenly decreased, possibly as a result of a brief reduction in average stellar radius amounting to −0.055%. At roughly the same time, the pulsation amplitude of Polaris underwent a marked change. Prior to 1963 the V amplitude was in excess of about 0.1 mag, possibly decreasing at a rate of 0.019 mag century−1. Following the hiatus of 1963–1966, the pulsation amplitude underwent a sharp decline and now appears to be erratic on a cycle‐to‐cycle basis, always smaller than 0.05 mag. The rapid rate of period increase for Polaris is consistent with a first crossing of the Cepheid instability strip, while the hiatus of 1963–1966 and sudden decrease in pulsation amplitude thereafter suggest that the star may have left the instability strip for first crossers at that time, leaving it near the center of the instability strip for Cepheids in higher crossing modes.