97 research outputs found
Periodic variations in the O-C diagrams of five pulsation frequencies of the DB white dwarf EC 20058-5234
Variations in the pulsation arrival time of five independent pulsation frequencies of the DB white dwarf
EC 20058â5234 individually imitate the effects of reflex motion induced by a planet or companion but are
inconsistent when considered in unison. The pulsation frequencies vary periodically in a 12.9 year cycle and
undergo secular changes that are inconsistent with simple neutrino plus photon-cooling models. The magnitude of
the periodic and secular variations increases with the period of the pulsations, possibly hinting that the corresponding
physical mechanism is located near the surface of the star. The phase of the periodic variations appears coupled
to the sign of the secular variations. The standards for pulsation-timing-based detection of planetary companions
around pulsating white dwarfs, and possibly other variables such as subdwarf B stars, should be re-evaluated.
The physical mechanism responsible for this surprising result may involve a redistribution of angular momentum
or a magnetic cycle. Additionally, variations in a supposed combination frequency are shown to match the sum
of the variations of the parent frequencies to remarkable precision, an expected but unprecedented confirmation
of theoretical predictions.Web of Scienc
Whole Earth Telescope discovery of a strongly distorted quadrupole pulsation in the largest amplitude rapidly oscillating Ap star
We present a new analysis of the rapidly oscillating Ap (roAp) star, 2MASS J19400781 â 4420093 (J1940;
V = 13.1). The star was discovered using SuperWASP broadband photometry to have a frequency of
176.39 dâ1 (2041.55 ”Hz; P = 8.2 min; Holdsworth et al. 2014a) and is shown here to have a peak-to-peak
amplitude of 34 mmag. J1940 has been observed during three seasons at the South African Astronomical Ob-
servatory, and has been the target of a Whole Earth Telescope campaign. The observations reveal that J1940 pulsates in a distorted quadrupole mode with unusual pulsational phase variations. A higher signal-to-noise ratio spectrum has been obtained since J1940âs first announcement, which allows us to classify the star as A7 Vp Eu(Cr). The observing campaigns presented here reveal no pulsations other than the initially detected frequency. We model the pulsation in J1940 and conclude that the pulsation is distorted by a magnetic field
of strength 1.5 kG. A difference in the times of rotational maximum light and pulsation maximum suggests a significant offset between the spots and pulsation axis, as can be seen in roAp stars
GJ 1252 b: A 1.2 R\u3csub\u3eâ\u3c/sub\u3e Planet Transiting An M3 Dwarf At 20.4 pc
We report the discovery of GJ 1252 b, a planet with a radius of 1.193 ± 0.074 Râ and an orbital period of 0.52 days around an M3-type star (0.381 ± 0.019 Mâ, 0.391 ± 0.020 Râ) located 20.385 ± 0.019 pc away. We use Transiting Exoplanet Survey Satellite (TESS) data, ground-based photometry and spectroscopy, Gaia astrometry, and high angular resolution imaging to show that the transit signal seen in the TESS data must originate from a transiting planet. We do so by ruling out all false-positive scenarios that attempt to explain the transit signal as originating from an eclipsing stellar binary. Precise Doppler monitoring also leads to a tentative mass measurement of 2.09 ± 0.56 Mâ. The host star proximity, brightness (V = 12.19 mag, K = 7.92 mag), low stellar activity, and the system\u27s short orbital period make this planet an attractive target for detailed characterization, including precise mass measurement, looking for other objects in the system, and planet atmosphere characterization
Wavelength-resolved Reverberation Mapping of quasar CTSC30.10: Dissecting MgII and FeII emission regions
We present the results of the reverberation monitoring aimed at MgII broad
line and FeII pseudocontinuum for the luminous quasar CTS C30.10 (z = 0.90052)
with the Southern African Large Telescope covering the years 2012-2021. We
aimed at disentangling the MgII and UV FeII variability and the first
measurement of UV FeII time delay for a distant quasar. We used several methods
for time-delay measurements and determined both FeII and MgII time delays as
well as performed a wavelength-resolved time delay study for a combination of
MgII and FeII in the 2700 - 2900 \AA restframe wavelength range. We obtain the
time delay for MgII of days in the rest frame, while
for FeII we have two possible solutions of days and
in the rest frame. Combining this result with the old
measurement of FeII UV time delay for NGC 5548 we discuss for the first time
the radius-luminosity relation for UV FeII with the slope consistent with
within uncertainties. Since FeII time delay has a shorter time-delay component
but lines are narrower than MgII, we propose that the line delay measurement is
biased towards the BLR part facing the observer, with the bulk of the Fe II
emission may arise from the more distant BLR region, one that is shielded from
the observer.Comment: 22 pages, 19 Figures, 6 Tables, Submitted to Astronomy and
Astrophysics, Comments are welcom
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