ABSTRACT
We present observations and analysis of 18 stripped-envelope supernovae observed during 2013–2018. This sample consists of five H/He-rich SNe, six H-poor/He-rich SNe, three narrow lined SNe ...Ic, and four broad lined SNe Ic. The peak luminosity and characteristic time-scales of the bolometric light curves are calculated, and the light curves modelled to derive 56Ni and ejecta masses (MNi and Mej). Additionally, the temperature evolution and spectral line velocity curves of each SN are examined. Analysis of the O i line in the nebular phase of eight SNe suggests their progenitors had initial masses <20 M⊙. The bolometric light curve properties are examined in combination with those of other SE events from the literature. The resulting data set gives the Mej distribution for 80 SE–SNe, the largest such sample in the literature to date, and shows that SNe Ib have the lowest median Mej, followed by narrow-lined SNe Ic, H/He-rich SNe, broad-lined SNe Ic, and finally gamma-ray burst SNe. SNe Ic-6/7 show the largest spread of Mej ranging from ∼1.2–11 M⊙, considerably greater than any other subtype. For all SE–SNe = 2.8 ± 1.5 M⊙ which further strengthens the evidence that SE–SNe arise from low-mass progenitors which are typically <5 M⊙ at the time of explosion, again suggesting MZAMS <25 M⊙. The low and lack of clear bimodality in the distribution implies <30 M⊙ progenitors and that envelope stripping via binary interaction is the dominant evolutionary pathway of these SNe.
ABSTRACT We present observations of SN 2015bn (=PS15ae = CSS141223-113342+004332 = MLS150211-113342+004333), a Type I superluminous supernova (SLSN) at redshift z = 0.1136. As well as being one of ...the closest SLSNe I yet discovered, it is intrinsically brighter ( ) and in a fainter galaxy ( ) than other SLSNe at . We used this opportunity to collect the most extensive data set for any SLSN I to date, including densely sampled spectroscopy and photometry, from the UV to the NIR, spanning −50 to +250 days from optical maximum. SN 2015bn fades slowly, but exhibits surprising undulations in the light curve on a timescale of 30-50 days, especially in the UV. The spectrum shows extraordinarily slow evolution except for a rapid transformation between +7 and +20-30 days. No narrow emission lines from slow-moving material are observed at any phase. We derive physical properties including the bolometric luminosity, and find slow velocity evolution and non-monotonic temperature and radial evolution. A deep radio limit rules out a healthy off-axis gamma-ray burst, and places constraints on the pre-explosion mass loss. The data can be consistently explained by a M stripped progenitor exploding with erg kinetic energy, forming a magnetar with a spin-down timescale of ∼20 days (thus avoiding a gamma-ray burst) that reheats the ejecta and drives ionization fronts. The most likely alternative scenario-interaction with ∼20 M of dense, inhomogeneous circumstellar material-can be tested with continuing radio follow-up.
We present radial velocity follow-up observations of K2-19, a compact planetary system hosting three planets, of which the two larger ones, K2-19b and K2-19c, are close to the 3:2 mean motion ...resonance. An analysis considering only the radial velocity measurements detects K2-19b, the larger and more massive planet in the system, with a mass of 54.8 ± 7.5M⊕ and provides a marginal detection of K2-19c, with a mass of Mc = 5.9+7.6-4.3 M⊕. We also used the TRADES code to simultaneously model both our RV measurements and the existing transit timing measurements. We derived a mass of 54.4 ± 8.9M⊕ for K2-19b and of 7.5+3.0-1.4M⊕ for K2-19c. For K2-19b, these masses are consistent with a previous determination that was principally based on a photodynamical analysis of the K2-19 light curve. Differences remain mainly in the mass determination of the more lightweight planet, driven likely by the limited precision of the RV measurements and possibly some as yet unrecognized systematics.
We announce the discovery of K2-139 b (EPIC 218916923 b), a transiting warm-Jupiter (Teq = 547 ± 25 K) on a 29-d orbit around an active (log R'_HK = -4.46 ± 0.06) K0V star in K2 Campaign 7. We derive ...the system's parameters by combining the K2 photometry with ground-based follow-up observations. With a mass of 0.387_-0.075^+0.083 M_J and radius of 0.808_-0.033^+0.034 R_J, K2-139 b is one of the transiting warm Jupiters with the lowest mass known to date. The planetary mean density of 0.91_-0.20^+0.24 g/cm^3 can be explained with a core of ~50 M⊕. Given the brightness of the host star (V = 11.653 mag), the relatively short transit duration (~5 h), and the expected amplitude of the Rossiter-McLaughlin effect (~25m/s), K2-139 is an ideal target to measure the spin-orbit angle of a planetary system hosting a warm Jupiter.
ABSTRACT
Boyajian’s star is an apparently normal main-sequence F-type star with a very unusual light curve. The dipping activity of the star, discovered during the Kepler mission, presents deep, ...asymmetric, and aperiodic events. Here we present high-resolution spectroscopic follow-up during some dimming events recorded post-Kepler observations, from ground-based telescopes. We analyse data from the HERMES, HARPS-N, and FIES spectrographs to characterize the stellar atmosphere and to put some constraints on the hypotheses that have appeared in the literature concerning the occulting elements. The star’s magnetism, if existing, is not extreme. The spots on the surface, if present, would occupy 0.02 per cent of the area, at most. The chromosphere, irrespective of the epoch of observation, is hotter than the values expected from radiative equilibrium, meaning that the star has some degree of activity. We find no clear evidence of the interstellar medium or exocoments being responsible for the dimmings of the light curve. However, we detect at 1–2σ level, a decrease of the radial velocity of the star during the first dip recorded after the Kepler observations. We claim the presence of an optically thick object with likely inclined and high impact parameter orbits that produces the observed Rossiter–McLaughlin effect.
Cyanobacteria blooms can complicate the economical or recreational use of waters. Many of the bloom forming species are also potential producers of harmful cyanotoxins. The standard method for ...quantifying phytoplankton biomass, based on inverted microscopy, has high accuracy and is the only one producing biomass results on taxonomic level, but it requires specialized expertise and is time-consuming. Phycocyanin (PC) pigment concentration has been proven as a useful proxy for the concentration of cyanobacteria. Since 2006, we have studied practical solutions of in-situ monitoring of cyanobacteria using PC fluorescence probes. We have studied two eutrophic lakes, Lake Littoistenjärvi and Lake Kuralanjärvi in southwestern Finland using stationary monitoring stations equipped with PC probes. The fluorescence results were compared to independent water samples analyzed using standard methods. The PC fluorescence was positively correlated to cyanobacteria biomass in both lakes. Using site-specific post-calibrations of biomass, PC fluorescence can be used to estimate the absolute biomass of cyanobacteria. The monitoring techniques used in these studies are an applicable and relatively low-cost method to monitor cyanobacteria abundance. With nearly real-time data transfer possibilities, they can be used in management and early warning applications to minimize the harmful effects of cyanobacteria blooms.
Due to the eutrophication of water bodies, large and intense phytoplankton blooms, most commonly associated to cyanobacteria, have been increasingly reported. Cyanobacteria blooms can cause negative ...socioeconomic effects or even pose a serious risk to human and animal health. To minimize possible harmful effects, the authorities need to monitor and report the bloom situations to the public. The standard laboratory methods for quantifying phytoplankton biomass are accurate, but have flaws in practical management use: specialized expertise is required, and they are time-consuming. We have tested practical solutions to monitor cyanobacteria nearly real-time by using probes measuring phycocyanin fluorescence, which can be used as a proxy for cyanobacteria biomass. In the basic application, a fluorescence probe is mounted in a datalogger monitoring station in the field and the results calibrated to cyanobacteria concentration are transferred via GSM to a web page available to the authorities and the public. To indicate the risk levels of cyanobacteria concentration to the public we have used a 3-scale ‘traffic light’ system. The automated monitoring station applications used in our studies, with nearly real-time web results, are an applicable and relatively low-cost method to monitor sensitive sites like water intakes, aquaculture and recreational areas.
Results from regular monitoring of relativistic compact binaries like PSR 1913+16 are consistent with the dominant (quadrupole) order emission of gravitational waves (GWs). We show that observations ...associated with the binary black hole (BBH) central engine of blazar OJ 287 demand the inclusion of gravitational radiation reaction effects beyond the quadrupolar order. It turns out that even the effects of certain hereditary contributions to GW emission are required to predict impact flare timings of OJ 287. We develop an approach that incorporates this effect into the BBH model for OJ 287. This allows us to demonstrate an excellent agreement between the observed impact flare timings and those predicted from ten orbital cycles of the BBH central engine model. The deduced rate of orbital period decay is nine orders of magnitude higher than the observed rate in PSR 1913+16, demonstrating again the relativistic nature of OJ 287's central engine. Finally, we argue that precise timing of the predicted 2019 impact flare should allow a test of the celebrated black hole "no-hair theorem" at the 10% level.
We present the results of our power spectral density analysis for the BL Lac object OJ 287, utilizing the Fermi-LAT survey at high-energy γ-rays, Swift-XRT in X-rays, several ground-based telescopes ...and the Kepler satellite in the optical, and radio telescopes at GHz frequencies. The light curves are modeled in terms of continuous-time autoregressive moving average (CARMA) processes. Owing to the inclusion of the Kepler data, we were able to construct for the first time the optical variability power spectrum of a blazar without any gaps across ∼6 dex in temporal frequencies. Our analysis reveals that the radio power spectra are of a colored-noise type on timescales ranging from tens of years down to months, with no evidence for breaks or other spectral features. The overall optical power spectrum is also consistent with a colored noise on the variability timescales ranging from 117 years down to hours, with no hints of any quasi-periodic oscillations. The X-ray power spectrum resembles the radio and optical power spectra on the analogous timescales ranging from tens of years down to months. Finally, the γ-ray power spectrum is noticeably different from the radio, optical, and X-ray power spectra of the source: we have detected a characteristic relaxation timescale in the Fermi-LAT data, corresponding to ∼150 days, such that on timescales longer than this, the power spectrum is consistent with uncorrelated (white) noise, while on shorter variability timescales there is correlated (colored) noise.
TWO HOT JUPITERS FROM K2 CAMPAIGN 4 Johnson, Marshall C.; Gandolfi, Davide; Fridlund, Malcolm ...
The Astronomical journal,
06/2016, Letnik:
151, Številka:
6
Journal Article
Recenzirano
Odprti dostop
ABSTRACT We confirm the planetary nature of two transiting hot Jupiters discovered by the Kepler spacecraft's K2 extended mission in its Campaign 4, using precise radial velocity measurements from ...FIES@NOT, HARPS-N@TNG, and the coudé spectrograph on the McDonald Observatory 2.7 m telescope. K2-29 b (EPIC 211089792b) transits a K1V star with a period of 3.2589263 0.0000015 days; its orbit is slightly eccentric ( e = 0.084 − 0.023 + 0.032 ). It has a radius of R P = 1.000 − 0.067 + 0.071 RJ and a mass of M P = 0.613 − 0.026 + 0.027 MJ. Its host star exhibits significant rotational variability, and we measure a rotation period of P rot = 10.777 0.031 days. K2-30 b (EPIC 210957318 b) transits a G6V star with a period of 4.098503 0.000011 days. It has a radius of R P = 1.039 − 0.051 + 0.050 RJ and a mass of M P = 0.579 − 0.027 + 0.028 MJ. The star has a low metallicity for a hot Jupiter host, Fe / H = − 0.15 0.05 .
PDF
