47 research outputs found
The beta Pictoris association: Catalog of photometric rotational periods of low-mass members and candidate members
We intended to compile the most complete catalog of bona fide members and
candidate members of the beta Pictoris association, and to measure their
rotation periods and basic properties from our own observations, public
archives, and exploring the literature. We carried out a multi-observatories
campaign to get our own photometric time series and collected all archived
public photometric data time series for the stars in our catalog. Each time
series was analyzed with the Lomb-Scargle and CLEAN periodograms to search for
the stellar rotation periods. We complemented the measured rotational
properties with detailed information on multiplicity, membership, and projected
rotational velocity available in the literature and discussed star by star. We
measured the rotation periods of 112 out of 117 among bona fide members and
candidate members of the beta Pictoris association and, whenever possible, we
also measured the luminosity, radius, and inclination of the stellar rotation
axis. This represents to date the largest catalog of rotation periods of any
young loose stellar association. We provided an extensive catalog of rotation
periods together with other relevant basic properties useful to explore a
number of open issues, such as the causes of spread of rotation periods among
coeval stars, evolution of angular momentum, and lithium-rotation connection.Comment: Forthcoming article, Received: 20 June 2016 / Accepted: 09 September
2016; 40 pages, 2 figures. The online figures A1-A73 are available at CD
A low energy core-collapse supernova without a hydrogen envelope
The final fate of massive stars depends on many factors, including mass,
rotation rate, magnetic fields and metallicity. Theory suggests that some
massive stars (initially greater than 25-30 solar masses) end up as Wolf-Rayet
stars which are deficient in hydrogen because of mass loss through strong
stellar winds. The most massive of these stars have cores which may form a
black hole and theory predicts that the resulting explosion produces ejecta of
low kinetic energy, a faint optical display and a small mass fraction of
radioactive nickel(1,2,3). An alternative origin for low energy supernovae is
the collapse of the oxygen-neon core of a relatively lowmass star (7-9 solar
masses) through electron capture(4,5). However no weak, hydrogen deficient,
core-collapse supernovae are known. Here we report that such faint, low energy
core-collapse supernovae do exist, and show that SN2008ha is the faintest
hydrogen poor supernova ever observed. We propose that other similar events
have been observed but they have been misclassified as peculiar thermonuclear
supernovae (sometimes labelled SN2002cx-like events(6)). This discovery could
link these faint supernovae to some long duration gamma-ray bursts. Extremely
faint, hydrogen-stripped core-collapse supernovae have been proposed to produce
those long gamma-ray bursts whose afterglows do not show evidence of
association with supernovae (7,8,9).Comment: Submitted 12 January 2009 - Accepted 24 March 200
Homogeneously derived transit timings for 17 exoplanets and reassessed TTV trends for WASP-12 and WASP-4
We homogeneously analyse ∼3.2 × 105 photometric measurements for ∼1100 transit lightcurves belonging to 17 exoplanet hosts. The photometric data cover 16 years 2004–2019 and include amateur and professional observations. Old archival lightcurves were reprocessed using up-to-date exoplanetary parameters and empirically debiased limb-darkening models. We also derive self-consistent transit and radial-velocity fits for 13 targets. We confirm the nonlinear TTV trend in the WASP-12 data at a high significance, and with a consistent magnitude. However, Doppler data reveal hints of a radial acceleration about ( − 7.5 ± 2.2) m/s/yr, indicating the presence of unseen distant companions, and suggesting that roughly 10 per cent of the observed TTV was induced via the light-travel (or Roemer) effect. For WASP-4, a similar TTV trend suspected after the recent TESS observations appears controversial and model-dependent. It is not supported by our homogeneus TTV sample, including 10 ground-based EXPANSION lightcurves obtained in 2018 simultaneously with TESS. Even if the TTV trend itself does exist in WASP-4, its magnitude and tidal nature are uncertain. Doppler data cannot entirely rule out the Roemer effect induced by possible distant companions
SN 2009N: linking normal and subluminous Type II-P Sne
We present ultraviolet, optical, near-infrared photometry and spectroscopy of
SN 2009N in NGC 4487. This object is a type II-P supernova with spectra
resembling those of subluminous II-P supernovae, while its bolometric
luminosity is similar to that of the intermediate luminosity SN 2008in. We
created SYNOW models of the plateau phase spectra for line identification and
to measure the expansion velocity. In the near-infrared spectra we find signs
indicating possible weak interaction between the supernova ejecta and the
pre-existing circumstellar material. These signs are also present in the
previously unpublished near-infrared spectra of SN 2008in. The distance to SN
2009N is determined via the expanding photosphere method and the standard
candle method as . The produced nickel-mass
is estimated to be . We infer the
physical properties of the progenitor at the explosion through hydrodynamical
modelling of the observables. We find the values of the total energy as , the ejected mass as , and the initial radius as .Comment: 23 pages, 18 figures, accepted for publication by MNRA
The nature of the late achromatic bump in GRB 120326A
The long gamma-ray burst GRB 120326A at redshift exhibited a multi-band light curve with a striking feature: a late-time, long-lasting achromatic rebrightening, rarely seen in such events. Peaking in optical and X-ray bands ks ( ks in the GRB rest frame) after the 70-s GRB prompt burst, the feature brightens nearly two orders of magnitude above the underlying optical power-law decay. Modelling the multiwavelength light curves, we investigate possible causes of the rebrightening in the context of the standard fireball model. We exclude a range of scenarios for the origin of this feature: reverse-shock flash, late-time forward shock peak due to the passage of the maximal synchrotron frequency through the optical band, late central engine optical/X-ray flares, interaction between the expanding blast wave and a density enhancement in the circumburst medium and gravitational microlensing. Instead we conclude that the achromatic rebrightening may be caused by a refreshed forward shock or a geometrical effect. In addition, we identify an additional component after the end of the prompt emission, that shapes the observed X-ray and optical light curves differently, ruling out a single overall emission component to explain the observed early time emission
Panchromatic Observations of the Textbook GRB 110205A: Constraining Physical Mechanisms of Prompt Emission and Afterglow
We present a comprehensive analysis of a bright, long-duration ( T 90 ~ 257 s) GRB 110205A at redshift z = 2.22. The optical prompt emission was detected by Swift /UVOT, ROTSE-IIIb, and BOOTES telescopes when the gamma-ray burst (GRB) was still radiating in the γ-ray band, with optical light curve showing correlation with γ-ray data. Nearly 200 s of observations were obtained simultaneously from optical, X-ray, to γ-ray (1 eV to 5 MeV), which makes it one of the exceptional cases to study the broadband spectral energy distribution during the prompt emission phase. In particular, we clearly identify, for the first time, an interesting two-break energy spectrum, roughly consistent with the standard synchrotron emission model in the fast cooling regime. Shortly after prompt emission (~1100 s), a bright ( R = 14.0) optical emission hump with very steep rise (α ~ 5.5) was observed, which we interpret as the reverse shock (RS) emission. It is the first time that the rising phase of an RS component has been closely observed. The full optical and X-ray afterglow light curves can be interpreted within the standard reverse shock (RS) + forward shock (FS) model. In general, the high-quality prompt and afterglow data allow us to apply the standard fireball model to extract valuable information, including the radiation mechanism (synchrotron), radius of prompt emission ( R GRB ~ 3 × 10 13 cm), initial Lorentz factor of the outflow (Γ 0 ~ 250), the composition of the ejecta (mildly magnetized), the collimation angle, and the total energy budget.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98559/1/0004-637X_751_2_90.pd
ExoClock Project. III. 450 New Exoplanet Ephemerides from Ground and Space Observations
The ExoClock project has been created to increase the efficiency of the Ariel mission. It will achieve this by continuously monitoring and updating the ephemerides of Ariel candidates, in order to produce a consistent catalog of reliable and precise ephemerides. This work presents a homogenous catalog of updated ephemerides for 450 planets, generated by the integration of ∼18,000 data points from multiple sources. These sources include observations from ground-based telescopes (the ExoClock network and the Exoplanet Transit Database), midtime values from the literature, and light curves from space telescopes (Kepler, K2, and TESS). With all the above, we manage to collect observations for half of the postdiscovery years (median), with data that have a median uncertainty less than 1 minute. In comparison with the literature, the ephemerides generated by the project are more precise and less biased. More than 40% of the initial literature ephemerides had to be updated to reach the goals of the project, as they were either of low precision or drifting. Moreover, the integrated approach of the project enables both the monitoring of the majority of the Ariel candidates (95%), and also the identification of missing data. These results highlight the need for continuous monitoring to increase the observing coverage of the candidate planets. Finally, the extended observing coverage of planets allows us to detect trends (transit-timing variations) for a sample of 19 planets. All the products, data, and codes used in this work are open and accessible to the wider scientific community
Discovery of a young low-mass brown dwarf transiting a fast-rotating F-type star by the Galactic Plane eXoplanet (GPX) survey
We announce the discovery of GPX-1 b, a transiting brown dwarf with a mass of
and a radius of
, the first sub-stellar object discovered by the Galactic
Plane eXoplanet (GPX) survey. The brown dwarf transits a moderately bright (
= 12.3 mag) fast-rotating F-type star with a projected rotational velocity
km/s. We use the isochrone placement algorithm to
characterize the host star, which has effective temperature K,
mass , radius
and approximate age Gyr. GPX-1 b has an orbital period
of 1.75 d, and a transit depth of %. We describe the GPX
transit detection observations, subsequent photometric and
speckle-interferometric follow-up observations, and SOPHIE spectroscopic
measurements, which allowed us to establish the presence of a sub-stellar
object around the host star. GPX-1 was observed at 30-min integrations by TESS
in Sector 18, but the data is affected by blending with a 3.4 mag brighter star
42 arcsec away. GPX-1 b is one of about two dozen transiting brown dwarfs known
to date, with a mass close to the theoretical brown dwarf/gas giant planet mass
transition boundary. Since GPX-1 is a moderately bright and fast-rotating star,
it can be followed-up by the means of Doppler tomography.Comment: 13 pages, 13 figures, accepted to MNRAS in May 202
The bright Type IIP SN 2009bw, showing signs of interaction
We present photometry and spectroscopy of the type IIP supernova 2009bw in
UGC 2890 from few days after the outburst to 241 days. The light curve of SN
2009bw during the photospheric phase is similar to that of normal SNe IIP but
with brighter peak and plateau (Mmax R = -17.82 mag, Mplateau R = -17.37 mag).
The luminosity drop from the photospheric to the nebular phase is one of the
fastest ever observed, ~2.2 mag in about 13 days. The radioactive tail of the
bolometric light curve indicates that the amount of ejected 56 Ni is \approx
0.022 M\odot. The photospheric spectra reveal high velocity lines of H{\alpha}
and H{\beta} until about 105 days after the shock breakout, suggesting a
possible early interaction between the SN ejecta and pre-existent circumstellar
material, and the presence of CNO elements. By modeling the bolometric light
curve, ejecta expansion velocity and photospheric temperature, we estimate a
total ejected mass of 8-12M\odot, a kinetic energy of ~0.3 foe and an initial
radius of ~ 3.6 - 7 \times 10^13 cm.Comment: Accepted for publication in MNRAS, 19 pages, 13 figures, 9 table