ABSTRACT
Detecting and understanding rotation in stellar interiors is nowadays one of the unsolved problems in stellar physics. Asteroseismology has been able to provide insights on rotation for the ...Sun, solar-like stars, and compact objects like white dwarfs. However, this is still very difficult for intermediate-mass stars. These stars are moderate-to-rapid rotators. Rotation splits and shifts the oscillation modes, which makes the oscillation spectrum more complex and harder to interpret. Here we study the oscillation patterns of a sample of benchmark δ Sct stars belonging to eclipsing binary systems with the objective of finding the frequency spacing related to the rotational splitting (δr). For this task, we combine three techniques: the Fourier transform, the autocorrelation function, and the histogram of frequency differences. The last two showed a similar behaviour. For most of the stars, it was necessary to determine the large separation (Δν) prior to spot δr. This is the first time we may clearly state that one of the periodicities present in the p modes oscillation spectra of δ Sct stars corresponds to the rotational splitting. This is true independent of the stellar rotation rate. These promising results pave the way to finding a robust methodology to determine rotational splittings from the oscillation spectra of δ Sct stars and, thus, understanding the rotational profile of intermediate-mass pulsating stars.
ABSTRACT
We present the results of a systematic search for new rapidly oscillating Ap (roAp) stars using the 2-min cadence data collected by the Transiting Exoplanet Survey Satellite (TESS) during ...its Cycle 1 observations. We identify 12 new roAp stars. Amongst these stars we discover the roAp star with the longest pulsation period, another with the shortest rotation period, and six with multiperiodic variability. In addition to these new roAp stars, we present an analysis of 44 known roAp stars observed by TESS during Cycle 1, providing the first high-precision and homogeneous sample of a significant fraction of the known roAp stars. The TESS observations have shown that almost 60 per cent (33) of our sample of stars are multiperiodic, providing excellent cases to test models of roAp pulsations, and from which the most rewarding asteroseismic results can be gleaned. We report four cases of the occurrence of rotationally split frequency multiplets that imply different mode geometries for the same degree modes in the same star. This provides a conundrum in applying the oblique pulsator model to the roAp stars. Finally, we report the discovery of non-linear mode interactions in α Cir (TIC 402546736, HD 128898) around the harmonic of the principal mode – this is only the second case of such a phenomenon.
Surveys have shown that super-Earth and Neptune-mass exoplanets are more frequent than gas giants around low-mass stars, as predicted by the core accretion theory of planet formation. We report the ...discovery of a giant planet around the very-low-mass star GJ 3512, as determined by optical and near-infrared radial-velocity observations. The planet has a minimum mass of 0.46 Jupiter masses, very high for such a small host star, and an eccentric 204-day orbit. Dynamical models show that the high eccentricity is most likely due to planet-planet interactions. We use simulations to demonstrate that the GJ 3512 planetary system challenges generally accepted formation theories, and that it puts constraints on the planet accretion and migration rates. Disk instabilities may be more efficient in forming planets than previously thought.
ABSTRACT
We present the results of a systematic search of the Transiting Exoplanet Survey Satellite (TESS) 2-min cadence data for new rapidly oscillating Ap (roAp) stars observed during the Cycle 2 ...phase of its mission. We find seven new roAp stars previously unreported as such and present the analysis of a further 25 roAp stars that are already known. Three of the new stars show multiperiodic pulsations, while all new members are rotationally variable stars, leading to almost 70 per cent (22) of the roAp stars presented being α2 CVn-type variable stars. We show that targeted observations of known chemically peculiar stars are likely to overlook many new roAp stars, and demonstrate that multiepoch observations are necessary to see pulsational behaviour changes. We find a lack of roAp stars close to the blue edge of the theoretical roAp instability strip, and reaffirm that mode instability is observed more frequently with precise, space-based observations. In addition to the Cycle 2 observations, we analyse TESS data for all-known roAp stars. This amounts to 18 further roAp stars observed by TESS. Finally, we list six known roAp stars that TESS is yet to observe. We deduce that the incidence of roAp stars amongst the Ap star population is just 5.5 per cent, raising fundamental questions about the conditions required to excite pulsations in Ap stars. This work, coupled with our previous work on roAp stars in Cycle 1 observations, presents the most comprehensive, homogeneous study of the roAp stars in the TESS nominal mission, with a collection of 112 confirmed roAp stars in total.
Context.
Teegarden’s Star is the brightest and one of the nearest ultra-cool dwarfs in the solar neighbourhood. For its late spectral type (M7.0 V), the star shows relatively little activity and is a ...prime target for near-infrared radial velocity surveys such as CARMENES.
Aims.
As part of the CARMENES search for exoplanets around M dwarfs, we obtained more than 200 radial-velocity measurements of Teegarden’s Star and analysed them for planetary signals.
Methods.
We find periodic variability in the radial velocities of Teegarden’s Star. We also studied photometric measurements to rule out stellar brightness variations mimicking planetary signals.
Results.
We find evidence for two planet candidates, each with 1.1
M
⊕
minimum mass, orbiting at periods of 4.91 and 11.4 d, respectively. No evidence for planetary transits could be found in archival and follow-up photometry. Small photometric variability is suggestive of slow rotation and old age.
Conclusions.
The two planets are among the lowest-mass planets discovered so far, and they are the first Earth-mass planets around an ultra-cool dwarf for which the masses have been determined using radial velocities.
Context.
The CARMENES instrument, installed at the 3.5 m telescope of the Calar Alto Observatory in Almería, Spain, was conceived to deliver high-accuracy radial velocity (RV) measurements with ...long-term stability to search for temperate rocky planets around a sample of nearby cool stars. Moreover, the broad wavelength coverage was designed to provide a range of stellar activity indicators to assess the nature of potential RV signals and to provide valuable spectral information to help characterise the stellar targets.
Aims.
We describe the CARMENES guaranteed time observations (GTO), spanning from 2016 to 2020, during which 19 633 spectra for a sample of 362 targets were collected. We present the CARMENES Data Release 1 (DR1), which makes public all observations obtained during the GTO of the CARMENES survey.
Methods.
The CARMENES survey target selection was aimed at minimising biases, and about 70% of all known M dwarfs within 10 pc and accessible from Calar Alto were included. The data were pipeline-processed, and high-level data products, including 18 642 precise RVs for 345 targets, were derived. Time series data of spectroscopic activity indicators were also obtained.
Results.
We discuss the characteristics of the CARMENES data, the statistical properties of the stellar sample, and the spectroscopic measurements. We show examples of the use of CARMENES data and provide a contextual view of the exoplanet population revealed by the survey, including 33 new planets, 17 re-analysed planets, and 26 confirmed planets from transiting candidate follow-up. A subsample of 238 targets was used to derive updated planet occurrence rates, yielding an overall average of 1.44 ± 0.20 planets with 1
M
⊕
<
M
pl
sin
i <
1000
M
⊕
and 1 day <
P
orb
< 1000 days per star, and indicating that nearly every M dwarf hosts at least one planet. All the DR1 raw data, pipeline-processed data, and high-level data products are publicly available online.
Conclusions.
CARMENES data have proven very useful for identifying and measuring planetary companions. They are also suitable for a variety of additional applications, such as the determination of stellar fundamental and atmospheric properties, the characterisation of stellar activity, and the study of exoplanet atmospheres.
δ
Scuti stars are intermediate-mass pulsators located in the classical Cepheid instability strip with spectral types ranging from A to F. In the last years, some authors found an amplitude and ...frequency modulation in some of these stars. In our work we have chosen the continuous wavelet transform as the more appropriate tool to perform a time-frequency analysis of the light curves of HD 174936 and HD 174966. We have chosen this tool because, unlike the short time Fourier transform, that uses a fixed windows size, the continuous wavelet transform uses short windows at high frequencies and long windows at low frequencies, making it like an adaptive analysis tool. In order to improve the resolution of the frequencies obtained by the continuous wavelet transform, we have also used the synchrosqueeze algorithm to “focus” the result. Then, we are capable to obtain a measure of the instantaneous frequencies of the signal in a wide range of frequencies. To check our results, we have compared them with the synchrosqueezed continuous wavelet transform of a synthetic signal generated with the frequencies previously obtained by a classical approach. Our results show that some frequencies are stable, at least within the observation run time, although some others show some kind of variation. This is the first time that such variations in the oscillation frequencies of HD 174936 and HD 174966 are reported.
Clinical biochemical markers of bone turnover are usually increased in Paget's disease. However, the analysis of "new" markers, such as serum bone alkaline phosphatase (BAP), carboxy-terminal ...propeptide of type I procollagen (PICP), tartrate-resistant acid phosphatase (TRAP), telopeptide carboxy-terminal propeptide of type I collagen (ICTP), and urinary pyridinoline (PYR) and deoxipyridinoline (D-PYR), may improve the diagnostic efficacy and the evaluation of Paget's disease compared with conventional markers, such as serum total alkaline phosphatase (TAP) and urinary hydroxyproline (HYP). To evaluate the diagnostic accuracy and the changes of biochemical markers of bone turnover according to Paget's disease activity, we measured the levels of all these markers in three groups of pagetic patients classified according to their serum TAP activity: G-I, patients with serum TAP lower than 250 U/l (upper limit) (n = 15); G-II, patients with serum TAP between 251 and 500 U/l (n = 18); and G-III, patients with serum TAP greater than 501 U/l (n = 26). Serum TAP and BAP showed the highest diagnostic accuracy among the markers of bone formation with a sensitivity of 78% and 84%, respectively, when the specificity was 100%. Urinary PYR was the most sensitive marker of bone resorption. Also, urinary PYR showed the highest proportion of increased values in pagetic patients (73%) compared with urinary HYP (64%), urinary D-PYR (60%), serum ICTP (41%), or serum TRAP (39%). In pagetic patients with normal serum TAP activity (G-I), serum BAP concentration was increased in 60% of patients, and urinary PYR was increased in 40% of patients.
In various experimental models, S-adenosylmethionine (SAMe) has been shown to reduce liver injury by preventing depletion of glutathione, one of the antioxidant systems that plays a critical role in ...defence against oxidative stress. On the other hand, alpha-tocopherol may be decreased in liver diseases, and treatment with this vitamin reduces liver injury in CCl(4)-treated rats. Since there is a close relationship among the different antioxidant systems (mainly glutathione, alpha-tocopherol and ascorbic acid), we have assessed whether, as well as restoring hepatic glutathione content, SAMe has any effect on liver alpha-tocopherol and ascorbic acid levels in CCl(4)-injured rats. Four groups of seven male Wistar rats treated for 9 weeks were studied: rats induced to cirrhosis with CCl(4), rats induced to cirrhosis plus SAMe administration (10 mg x kg(-1) x day(-1)) and their respective controls. Liver samples were obtained for measuring levels of glutathione, alpha-tocopherol, ascorbic acid and thiobarbituric acid-reactive substances (TBARS), and hydroxyproline concentration as an index of collagen content. The hydroxyproline content was higher in CCl(4)-injured rats than in the control group (4.4+/-1.8 and 1.1+/-0.3 micromol/g respectively; P<0.05). In CCl(4)-injured rats, SAMe administration decreased collagen content (2.7+/-1.0 microl/g; P<0.05) and TBARS, and corrected glutathione depletion. alpha-Tocopherol was significantly lower in CCl(4)-injured rats than in controls (17.3+/-4.9 and 23.0+/-4.0 micromol/g respectively; P<0.05). By contrast, alpha-tocopherol levels were similar (23.8+/-5.1 micromol/g) in CCl(4)-injured rats receiving SAMe and in controls. In CCl(4)-injured rats, liver ascorbic acid was decreased in comparison with controls (4.9+/-1.8 and 8.2+/-1.0 micromol/g respectively; P<0.05), levels which were not replenished by SAMe (4.6+/-0.4 micromol/g). In conclusion, SAMe not only decreases fibrosis and protects against hepatic glutathione depletion, but has a further antioxidant effect of preventing alpha-tocopherol depletion in CCl(4)-injured rats.
We present the results of a systematic search of the Transiting Exoplanet Survey Satellite (TESS) 2-min cadence data for new rapidly oscillating Ap (roAp) stars observed during the Cycle 2 phase of ...its mission. We find seven new roAp stars previously unreported as such and present the analysis of a further 25 roAp stars that are already known. Three of the new stars show multiperiodic pulsations, while all new members are rotationally variable stars, leading to almost 70 per cent (22) of the roAp stars presented being \(\alpha^2\) CVn-type variable stars. We show that targeted observations of known chemically peculiar stars are likely to overlook many new roAp stars, and demonstrate that multi-epoch observations are necessary to see pulsational behaviour changes. We find a lack of roAp stars close to the blue edge of the theoretical roAp instability strip, and reaffirm that mode instability is observed more frequently with precise, space-based observations. In addition to the Cycle 2 observations, we analyse TESS data for all known roAp stars. This amounts to 18 further roAp stars observed by TESS. Finally, we list six known roAp stars that TESS is yet to observe. We deduce that the incidence of roAp stars amongst the Ap star population is just 5.5 per cent, raising fundamental questions about the conditions required to excite pulsations in Ap stars. This work, coupled with our previous work on roAp stars in Cycle 1 observations, presents the most comprehensive, homogeneous study of the roAp stars in the TESS nominal mission, with a collection of 112 confirmed roAp stars in total.
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