Previous studies have found that red giants (RGs) in close binary systems undergoing spin-orbit resonance exhibit an enhanced level of magnetic activity with respect to single RGs rotating at the ...same rate, from measurements of photometric variability, S ph ′ , and the chromospheric emission S -index, S Ca II . Here, we consider a sample of 4465 RGs observed by the NASA Kepler mission, for which previous studies have measured S ph ′ and S Ca II , in order to measure additional activity indicators that probe different heights in the chromosphere: the near-ultraviolet (NUV) excess from NASA GALEX photometric data, and chromospheric indices based on the depth of H α , Mg I , and infared Ca II absorption lines from LAMOST spectroscopic data. Firstly, as for Ca II H&K, we observe that RGs belonging to close binaries in a state of spin-orbit resonance display larger chromospheric emission than the cohort of RGs, as is illustrated by an NUV excess and shallower H α and infrared Ca II lines. We report no excess of Mg I emission. This result reinforces previous claims that tidal locking leads to enhanced magnetic fields, and allows us to provide criteria to classify active RGs – single or binary – based on their rotation periods and magnetic activity indices. Secondly, we strikingly observe that the depths of the Mg I and H α lines are anticorrelated and correlated, respectively, with the amplitude of solar-like oscillations for a given surface gravity, log g , regardless of the presence of photometric rotational modulation. Such a correlation opens up future possibilities of estimating the value of magnetic fields at the surface of RG stars, whether quiet or active, by combining spectroscopic and asteroseismic measurements with three-dimensional atmospheric models that include radiative transfer.
Given its peak luminosity and early-time spectra, ASASSN-15lh was classified as the most luminous supernova ever discovered. Here, we report a UV rebrightening of ASASSN-15lh observed with Swift ...during our follow-up campaign. The rebrightening began at t ... 90 d (observer frame) after the primary peak and was followed by a ~120-d long plateau in the bolometric luminosity, before starting to fade again at t ... 210 d. ASASSN-15lh rebrightened in the Swift UV bands by ...mUVW2 ... -1.75 mag, ...mUVM2 ... -1.25 mag and ...mUVW1 ... -0.8 mag, but did not rebrighten in the optical bands. Throughout its initial decline, subsequent rebrightening and renewed decline, the spectra did not show evidence of interactions between the ejecta and circumstellar medium such as narrow emission lines. There are hints of weak Ha emission at late-times, but Margutti et al. have shown that it is narrow line emission consistent with star formation in the host nucleus. By fitting a blackbody, we find that during the rebrightening, the effective photospheric temperature increased from TBB ... 11 000 K to TBB ... 18 000 K. Over the ~ 550 d since its detection, ASASSN-15lh has radiated ~1.7 -1.9 x 10 super( 52) erg. Although its physical nature remains uncertain, the evolution of ASASSN-15lh's photospheric radius, its radiated energy and the implied event rate, are all more similar to those of H-poor superluminous supernovae than to tidal disruption events. (ProQuest: ... denotes formulae/symbols omitted.)
We present ground-based and Swift photometric and spectroscopic observations of the tidal disruption event (TDE) ASASSN-15oi, discovered at the centre of 2MASX J20390918-3045201 (d ... 216 Mpc) by ...the All-Sky Automated Survey for SuperNovae. The source peaked at a bolometric luminosity of L ... 1.3 x 10 super( 44) erg s... and radiated a total energy of E ... 6.6 x 1050 erg over the first ~3.5 months of observations. The early optical/UV emission of the source can be fit by a blackbody with temperature increasing from T ~ 2 x 10 super( 4) K to T ~ 4 x 10 super( 4) K while the luminosity declines from L ... 1.3 x 10 super( 44) erg s... to L ... 2.3 x 10 super( 43) erg s..., requiring the photosphere to be shrinking rapidly. The optical/UV luminosity decline during this period is most consistent with an exponential decline, ..., with t ... 46.5 d for t0 ... 57241.6 (MJD), while a power-law decline of L ... (t - t0)-a with t sub( 0) ... 57 212.3 and a = 1.62 provides a moderately worse fit. ASASSN-15oi also exhibits roughly constant soft X-ray emission that is significantly weaker than the optical/UV emission. Spectra of the source show broad helium emission lines and strong blue continuum emission in early epochs, although these features fade rapidly and are not present ~3 months after discovery. The early spectroscopic features and colour evolution of ASASSN-15oi are consistent with a TDE, but the rapid spectral evolution is unique among optically selected TDEs. (ProQuest: ... denotes formulae/symbols omitted.)
The ASAS-SN bright supernova catalogue – II. 2015 Holoien, T. W.-S; Brown, J. S; Stanek, K. Z ...
Monthly notices of the Royal Astronomical Society,
05/2017, Letnik:
467, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Abstract
This manuscript presents information for all supernovae discovered by the All-Sky Automated Survey for SuperNovae (ASAS-SN) during 2015, its second full year of operations. The same ...information is presented for bright (mV ≤ 17), spectroscopically confirmed supernovae discovered by other sources in 2015. As with the first ASAS-SN bright supernova catalogue, we also present redshifts and near-ultraviolet through infrared magnitudes for all supernova host galaxies in both samples. Combined with our previous catalogue, this work comprises a complete catalogue of 455 supernovae from multiple professional and amateur sources, allowing for population studies that were previously impossible. This is the second of a series of yearly papers on bright supernovae and their hosts from the ASAS-SN team.
Abstract
Solar-type stars are born with relatively rapid rotation and strong magnetic fields. Through a process known as magnetic braking, the rotation slows over time as stellar winds gradually ...remove angular momentum from the system. The rate of angular momentum loss depends sensitively on the magnetic morphology, with the dipole field exerting the largest torque on the star. Recent observations suggest that the efficiency of magnetic braking may decrease dramatically in stars near the middle of their main-sequence lifetimes. One hypothesis to explain this reduction in efficiency is a shift in magnetic morphology from predominantly larger to smaller spatial scales. We aim to test this hypothesis with spectropolarimetric measurements of two stars that sample chromospheric activity levels on opposite sides of the proposed magnetic transition. As predicted, the more active star (HD 100180) exhibits a significant circular polarization signature due to a nonaxisymmetric large-scale magnetic field, while the less active star (HD 143761) shows no significant signal. We identify analogs of the two stars among a sample of well-characterized
Kepler
targets, and we predict that the asteroseismic age of HD 143761 from future
Transiting Exoplanet Survey Satellite
observations will substantially exceed the age expected from gyrochronology. We conclude that a shift in magnetic morphology likely contributes to the loss of magnetic braking in middle-aged stars, which appears to coincide with the shutdown of their global dynamos.
Abstract
This catalogue summarizes information for all supernovae discovered by the All-Sky Automated Survey for SuperNovae (ASAS-SN) and all other bright (m
peak ≤ 17), spectroscopically confirmed ...supernovae discovered in 2016. We then gather the near-infrared through ultraviolet magnitudes of all host galaxies and the offsets of the supernovae from the centres of their hosts from public data bases. We illustrate the results using a sample that now totals 668 supernovae discovered since 2014 May 1, including the supernovae from our previous catalogues, with type distributions closely matching those of the ideal magnitude limited sample from Li et al. This is the third of a series of yearly papers on bright supernovae and their hosts from the ASAS-SN team.
TOI-1416 (BD+42 2504, HIP 70705) is a
V
=10 late G- or early K-type dwarf star. TESS detected transits in its Sectors 16, 23, and 50 with a depth of about 455 ppm and a period of 1.07 days. Radial ...velocities (RVs) confirm the presence of the transiting planet TOI-1416
b
, which has a mass of 3.48 ± 0.47
M
⊕
and a radius of 1.62 ± 0.08
R
⊕
, implying a slightly sub-Earth density of 4.50
−0.83
+0.99
g cm
−3
. The RV data also further indicate a tentative planet,
c
, with a period of 27.4 or 29.5 days, whose nature cannot be verified due to strong suspicions of contamination by a signal related to the Moon’s synodic period of 29.53 days. The nearly ultra-short-period planet TOI-1416
b
is a typical representative of a short-period and hot (
T
eq
≈ 1570 K) super-Earth-like planet. A planet model of an interior of molten magma containing a significant fraction of dissolved water provides a plausible explanation for its composition, and its atmosphere could be suitable for transmission spectroscopy with JWST. The position of TOI-1416
b
within the radius-period distribution corroborates the idea that planets with periods of less than one day do not form any special group. It instead implies that ultra-short-period planets belong to a continuous distribution of super-Earth-like planets with periods ranging from the shortest known ones up to ≈30 days; their period-radius distribution is delimited against larger radii by the Neptune Desert and by the period-radius valley that separates super-Earths from sub-Neptune planets. In the abundance of small, short-periodic planets, a notable plateau has emerged between periods of 0.6–1.4 days, which is compatible with the low-eccentricity formation channel. For the Neptune Desert, its lower limits required a revision due to the increasing population of short-period planets; for periods shorter then 2 days, we establish a radius of 1.6
R
⊕
and a mass of 0.028
M
jup
(corresponding to 8.9
M
⊕
) as the desert’s lower limits. We also provide corresponding limits to the Neptune Desert against the planets’ insolation and effective temperatures.
A soil quality database (SQDB) is a collection of soil samples described by a given set of parameters, allowing farmers, scientists and other stakeholders to make informed decisions about practices, ...processes and policies for soil use and management. If each parameter is considered as a dimension of the space spanned by the SQDB, extracting information becomes a difficult task when the number of parameters is >3. A widely used approach to explore multidimensional data sets is the self‐organizing map (SOM) method, which is suitable for clustering, visualization and extraction of information from multidimensional data. We applied the SOM method as an exploratory technique to an unlabelled SQDB to extract knowledge – data patterns and data associations – from the data set (the time and location of each sample were unknown). The SQDB used in this study is a set of 1240 unlabelled samples within the Central Valley of Chile, covering ca 7500 km². The predominant soils are Andisols with a large organic matter content (7–12%), small bulk densities (0.6–1.0 g/cm³) and large water‐holding capacity. We identified three patterns: (i) isolated region within the map with close neurons (smooth transitions), (ii) two or more regions with predominantly large or small values and (iii) homogeneous map with small values with an isolated region of large values. These patterns show that the data set represented more than two groups that were not necessarily related. For pH, no important associations with other investigated parameters were observed. Previous studies carried out by the local agricultural research station showed that pH values below 5.5 constrain nutrient uptake. Thus, locations presenting pH<5,5 should be subject to seasonal monitoring to assess management practices that mitigate soil acidity. The component plane for organic matter indicates that ca. 50% of the soil samples had contents <8% related to soil series characteristics and management practices. As the k‐means is initialized by random partitions, the two‐step approach (clustering the map representing the input data) is less sensitive to variations in the input data (subsamples) than is the direct application of k‐means to the input data, but it also reduces the computational cost. The ability of SOMs to visualize multidimensional data sets helps gain an understanding of the data in the exploratory phase, such as the association and integration of physical, chemical and biological parameters.
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