A dragon’s flame of many colours: multiwavelength observations of flares from the active M binary CR Draconis

Context. The Transiting Exoplanet Survey Satellite (TESS) provides us with high-precision photometric observations of large numbers of bright stars over more than 70% of the entire sky, allowing us to revisit and characterise well-known stars. Aims. We aim to conduct an asteroseismic analysis of the γ Doradus (γ Dor) star HD 112429 using both the available ground-based spectroscopy and TESS photometry, and assess the conditions required to measure the near-core rotation rate and buoyancy travel time. Methods. We collected and reduced the available five sectors of short-cadence TESS photometry of this star, as well as 672 legacy observations from six medium- to high-resolution ground-based spectrographs. We determined the stellar pulsation frequencies from both data sets using iterative prewhitening, did asymptotic g mode modelling of the star, and investigated the corresponding spectral line profile variations using the pixel-by-pixel method. Results. We validate the pulsation frequencies from the TESS data down to S/N ≥ 5.6, confirming recent reports in the literature that the classical criterion S/N ≥ 4 does not suffice for space-based observations. We identify the pulsations as prograde dipole g modes and r-mode pulsations, and measure a near-core rotation rate of 1.536 (3) d−1 and a buoyancy travel time Π0 of 4190 (50) s. These results are in agreement with the observed spectral line profile variations, which were qualitatively evaluated using a newly developed toy model. We establish a set of conditions that have to be fulfilled for an asymptotic asteroseismic analysis of g-mode pulsators. In the case of HD 112429, two TESS sectors of space photometry suffice. Conclusions. Although a detailed asteroseismic modelling analysis is not viable for g-mode pulsators with only short or sparse light curves of space photometry, it is possible to determine global asteroseismic quantities for a subset of these stars. Thanks to the ongoing TESS mission, this will allow us to characterise many more stars than only those with years of data.

NASA’s Transiting Exoplanet Survey Satellite (TESS) mission has been uncovering a growing number of exoplanets orbiting nearby, bright stars. Most exoplanets that have been discovered by TESS orbit narrow-line, slow-rotating stars, facilitating the confirmation and mass determination of these worlds. We present the discovery of a hot Jupiter orbiting a rapidly rotating ( km s−1) early F3V-dwarf, HD 115447 (TOI-778). The transit signal taken from Sectors 10 and 37 of TESS's initial detection of the exoplanet is combined with follow-up ground-based photometry and velocity measurements taken from Minerva-Australis, TRES, CORALIE, and CHIRON to confirm and characterize TOI-778 b. A joint analysis of the light curves and the radial velocity measurements yields a mass, a radius, and an orbital period for TOI-778 b of M J, 1.370 ± 0.043 R J, and ∼4.63 days, respectively. The planet orbits a bright (V = 9.1 mag) F3-dwarf with M = 1.40 ± 0.05 M ⊙, R = 1.70 ± 0.05 R ⊙, and . We observed a spectroscopic transit of TOI-778 b, which allowed us to derive a sky-projected spin–orbit angle of 18° ± 11°, consistent with an aligned planetary system. This discovery demonstrates the capability of smaller-aperture telescopes such as Minerva-Australis to detect the radial velocity signals produced by planets orbiting broad-line, rapidly rotating stars.

We present space-based ultraviolet/optical photometry and spectroscopy with the Swift Ultra-Violet/Optical Telescope and Hubble Space Telescope (HST), respectively, along with ground-based optical photometry and spectroscopy and near-infrared spectroscopy of supernova SN 2017erp. The optical light curves and spectra are consistent with a normal SN Ia. Compared to previous photometric samples in the near-ultraviolet (NUV), SN 2017erp has UV colors that are redder than NUV-blue SNe Ia corrected to similar optical colors. The chromatic difference between SNe 2011fe and 2017erp is dominated by the intrinsic differences in the UV rather than the expected dust reddening. This chromatic difference is similar to the SALT2 color law, derived from rest-frame ultraviolet photometry of higher redshift SNe Ia. Differentiating between intrinsic UV diversity and dust reddening can have important consequences for determining cosmological distances with rest-frame ultraviolet photometry. This ultraviolet spectroscopic series is the first from HST of a normal, albeit reddened, NUV-red SN Ia and is important for analyzing SNe Ia with intrinsically redder NUV colors. We show model comparisons suggesting that metallicity could be the physical difference between NUV-blue and NUV-red SNe Ia, with emission peaks from reverse fluorescence near 3000 Å implying a factor of ∼10 higher metallicity in the upper layers of SN 2017erp compared to SN 2011fe. Metallicity estimates are very model dependent, however, and there are multiple effects in the UV. Further models and UV spectra of SNe Ia are needed to explore the diversity of SNe Ia, which show seemingly independent differences in the near-UV peaks and mid-UV flux levels.

We report the discovery of a close-in (P orb = 3.349 days) warm Neptune with clear transit timing variations (TTVs) orbiting the nearby (d = 47.3 pc) active M4 star, TOI-2015. We characterize the planet's properties using Transiting Exoplanet Survey Satellite (TESS) photometry, precise near-infrared radial velocities (RVs) with the Habitable-zone Planet Finder Spectrograph, ground-based photometry, and high-contrast imaging. A joint photometry and RV fit yields a radius Rp=3.37−0.20+0.15R⊕ , mass mp=16.4−4.1+4.1M⊕ , and density ρp=2.32−0.37+0.38gcm−3 for TOI-2015 b, suggesting a likely volatile-rich planet. The young, active host star has a rotation period of P rot = 8.7 ± 0.9 days and associated rotation-based age estimate of 1.1 ± 0.1 Gyr. Though no other transiting planets are seen in the TESS data, the system shows clear TTVs of super-period Psup≈430days and amplitude ∼100 minutes. After considering multiple likely period-ratio models, we show an outer planet candidate near a 2:1 resonance can explain the observed TTVs while offering a dynamically stable solution. However, other possible two-planet solutions—including 3:2 and 4:3 resonances—cannot be conclusively excluded without further observations. Assuming a 2:1 resonance in the joint TTV-RV modeling suggests a mass of mb=13.3−4.5+4.7M⊕ for TOI-2015 b and mc=6.8−2.3+3.5M⊕ for the outer candidate. Additional transit and RV observations will be beneficial to explicitly identify the resonance and further characterize the properties of the system.

We present ground-based optical transmission spectroscopy of the low-density hot Jupiter WASP-88b covering the wavelength range of 4413−8333 Å with the FOcal Reducer Spectrograph (FORS2) on the Very Large Telescope. The FORS2 white light curves exhibit a significant time-correlated noise that we model using a Gaussian process and remove as a wavelength-independent component from the spectroscopic light curves. We analyse complementary photometric observations from the Transiting Exoplanet Survey Satellite and refine the system properties and ephemeris. We find a featureless transmission spectrum with increased absorption towards shorter wavelengths. We perform an atmospheric retrieval analysis with the aura code, finding tentative evidence for haze in the upper atmospheric layers and a lower likelihood for a dense cloud deck. While our retrieval analysis results point towards clouds and hazes, further evidence is needed to definitively reject a clear-sky scenario.

We report on Transiting Exoplanet Survey Satellite (TESS) high-precision photometry of the iconic non-eclipsing 5.60 days (O9.7Iab+black hole) binary Cygnus X-1. Previous ground-based photometry reveals low-amplitude (∼0.04 mag) ellipsoidal light-variations that arise from the tidal (and rotational) distortion of the O9.7Iab companion. Additional small light-variations have also been reported by many observers. Short-cadence TESS photometry was conducted over ∼27 days during 2019 July–August. The photometry shows the expected ∼5.60 days binary ellipsoidal variations, but in addition ∼0.01–0.03 mag complex quasi-periodic brightness variations. The observations were analyzed to investigate the underlying extra-binary variability. We also determined a new time of minimum light and calculated an updated period and light elements. The quasi-periodic, (non-binary) light-variations likely arise from the complex pulsations of the blue supergiant.

We report the discovery of TOI-2180 b, a 2.8 M J giant planet orbiting a slightly evolved G5 host star. This planet transited only once in Cycle 2 of the primary Transiting Exoplanet Survey Satellite (TESS) mission. Citizen scientists identified the 24 hr single-transit event shortly after the data were released, allowing a Doppler monitoring campaign with the Automated Planet Finder telescope at Lick Observatory to begin promptly. The radial velocity observations refined the orbital period of TOI-2180 b to be 260.8 ± 0.6 days, revealed an orbital eccentricity of 0.368 ± 0.007, and discovered long-term acceleration from a more distant massive companion. We conducted ground-based photometry from 14 sites spread around the globe in an attempt to detect another transit. Although we did not make a clear transit detection, the nondetections improved the precision of the orbital period. We predict that TESS will likely detect another transit of TOI-2180 b in Sector 48 of its extended mission. We use giant planet structure models to retrieve the bulk heavy-element content of TOI-2180 b. When considered alongside other giant planets with orbital periods over 100 days, we find tentative evidence that the correlation between planet mass and metal enrichment relative to stellar is dependent on orbital properties. Single-transit discoveries like TOI-2180 b highlight the exciting potential of the TESS mission to find planets with long orbital periods and low irradiation fluxes despite the selection biases associated with the transit method.

Based on the X-ray observations from XMM–Newton and Swift, and optical observations from Transiting Exoplanet Survey Satellite (TESS) and AAVSO, we present temporal and spectral properties of probable intermediate polar SWIFT J0503.7-2819. The X-ray light curve shows two distinctive features, where possibly the second pole seems to be active during the middle of the XMM–Newton observations. Present analysis confirms and also refines the previously reported orbital period of SWIFT J0503.7-2819 as 81.65 ± 0.04 min. The X-ray and optical variations of this target have been found to occur at the period of ∼65 min, which we propose as the spin period of the white dwarf. The energy-dependent modulation at this period, which are due to the photoelectric absorption in the accretion flow, also assures this conjecture. Two-temperature thermal plasma model well explains the X-ray spectra with temperatures of ∼150 eV and ∼18.5 keV, which is absorbed by a dense material with an average equivalent hydrogen column density of 3.8 × 1022 cm−2 that partially covers ∼27 per cent of the X-ray source. An attempt is made to understand the accretion flow in this system using the present data of SWIFT J0503.7-2819. If the proposed spin period is indeed the actual period, then SWIFT J0503.7-2819 could be the first nearly synchronous intermediate polar below the period gap.

Aims. We model the atmosphere of the ultra-hot Jupiter (UHJ) WASP-178b while accounting for non-local thermodynamical equilibrium (NLTE) effects and compare synthetic transmission spectra with near-ultraviolet (NUV) and optical observations. Methods. We used the HELIOS code (LTE) in the lower atmosphere and the ClOUDY code (LTE or NLTE) in the middle and upper atmosphere to compute the temperature-pressure (TP) and abundance profiles. We further used CLOUDY to compute the theoretical planetary transmission spectrum both in LTE and NLTE for comparison with observations. Results. We find an isothermal TP profile at pressures higher than 10 mbar and lower than 10−8 bar, with an almost linear increase from ∼2200 K to ∼8100 K in between. The temperature structure is driven by NLTE effects, particularly in the form of increased heating resulting from the overpopulation of long-lived FeII levels with strong transitions in the NUV band, where the stellar emission is strong, and of decreased cooling due to the underpopulation of MgI and MgII levels that dominate the cooling. The planetary atmosphere is hydrostatic up to pressures of ∼1 nbar, and thus accurately modelling spectral lines forming at pressures lower than ∼1 nbar requires accounting for both hydrodynamics and NLTE effects. The NLTE synthetic transmission spectrum overestimates the observed Hα and Hβ absorption, while the LTE model is in good agreement, which is surprising because the opposite has been found for the other UHJs for which NLTE modelling has been performed. In the NUV, we find an excellent match between the NLTE transmission spectrum and the HST/UVIS data, contrary to the LTE model. This contrasts with previous LTE results requiring SiO absorption to fit the observations. Conclusions. The accurate characterisation of the atmosphere of UHJs is possible only when accounting for NLTE effects and particularly for the level population of Fe and Mg, which respectively dominate heating and cooling.

We present a pilot method to estimate the high-mass initial mass function (IMF) across the arm, interarm, and spur regions in galaxies and apply it to NGC 628. We extracted star-forming complexes (SFCs) from the Hα Very Large Telescope/Multi Unit Spectroscopic Explorer and Ultraviolet Imaging Telescope (far-ultraviolet (FUV) and near-ultraviolet (NUV)) observations of NGC 628 and used Atacama Large Millimeter/submillimeter Array observations to define the molecular gas distribution. We find that the extinction-corrected Hα and FUV luminosities correlate well. Using the fact that O stars have a shorter lifetime (107 yr) compared to B stars (108 yr), we estimated the approximate number of O stars from Hα emission, and the number of B0 (M * > 10M ⊙), and B1 (10M ⊙ ≥ M * ≥ 3M ⊙) stars using FUV and NUV observations. We derived the IMF index (α) for different regions using O to B0 (α 1) and B0 to B1 (α 2) stellar ratios. Our findings indicate that if we assume Hα arises only from O8-type stars, the resulting α 1 value is consistent with the canonical IMF index. It steepens when we assume O stars with masses up to 100 M ⊙ with mean α 1 = 3.16 ± 0.62. However, the α 2 does not change for large variations in the O-star population, and the mean α = 2.64 ± 0.14. When we include only blue SFCs (FUV − NUV ≤ 0.3), mean α 2 is 2.43 ± 0.06. The IMF variation for SFCs in arms and spurs is insignificant. We also find that α 2 correlates with different properties of the SFCs, the most prominent being the extinction-corrected UV color (FUV − NUV).

We present results from simultaneous far-ultraviolet (FUV) and near-ultraviolet (NUV) observations of T Tauri stars (TTSs) in the Taurus molecular cloud with UVIT/AstroSat. This is the very first UVIT study of TTSs. From the spectral energy distribution of TTSs from FUV to IR, we show that classical TTSs (CTTSs) emit significantly higher UV excess compared to weak-line TTSs (WTTSs). The equivalent blackbody temperatures corresponding to the UV excess in CTTSs (>104 K) are also found to be relatively higher than those in WTTSs (<9250 K). From the UV excess, we have reclassified two WTTSs (BS Tau and V836 Tau) as CTTSs, which has been supported by the follow-up optical spectroscopic study using the Himalayan Chandra Telescope, showing strong Hα line emission. We find that CTTSs show strong excess emission in both the FUV (>107) and NUV (>103) bands, while WTTSs show strong excess only in the FUV (≲105), suggesting that excess emission in the NUV can be used as a tool to classify the TTSs. We also find a linear correlation between UV luminosity (a primary indicator of mass accretion) and Hα luminosity (a secondary indicator of mass accretion) with a slope of 1.20 ± 0.22 and intercept of 2.16 ± 0.70.

We present Hubble Space Telescope (HST) imagery, and ground-based spectroscopy and CCD photometry of the active galaxy Markarian 421 and its companion galaxy 14 arcsec to the ENE. The HST images indicate that the companion is a morphological spiral rather than elliptical as previous ground-based imaging has concluded. The companion has a bright, compact nucleus, appearing unresolved in the HST images. This is suggestive of Seyfert activity, or possibly a highly luminous compact star cluster. We also report the results of high dynamic range long-slit spectroscopy with the slit placed to extend across both galaxies and nuclei. Velocities derived from a number of absorption lines visible in both galaxies indicate that the two systems are probably tidally bound and thus in close physical proximity. Using the measured relative velocities, we derive a lower limit on the MKN 421 mass within the companion orbit (R∼10 kpc) of 5.9×1011 solar masses, and a mass-to-light ratio of ⩾17. Our spectroscopy also shows for ...

We present 16 new, and confirm 7 previously identified, DA white dwarfs in the Kepler field through ground-based spectroscopy with the Hale 200", Kitt Peak 4-meter, and Bok 2.3-meter telescopes. Using atmospheric models we determine their effective temperatures and surface gravities to constrain their position with respect to the ZZ Ceti (DA pulsator) instability strip, and look for the presence or absence of pulsation with Kepler's unprecedented photometry. Our results are as follows: i) From our measurements of temperature and surface gravity, 12 of the 23 DA white dwarfs from this work fall well outside of the instability strip. The Kepler photometry available for 11 of these WDs allows us to confirm that none are pulsating. One of these eleven happens to be a presumed binary, KIC 11604781, with a period of ~5 days. ii) The remaining 11 DA white dwarfs are instability strip candidates, potentially falling within the current, empirical instability strip, after accounting for uncertainties. These WDs will help constrain the strip's location further, as eight are near the blue edge and three are near the red edge of the instability strip. Four of these WDs do not have Kepler photometry, so ground-based photometry is needed to determine the pulsation nature of these white dwarfs. The remaining seven have Kepler photometry available, but do not show any periodicity on typical WD pulsation timescales.

We have examined the behavior of a number of bolides in Earth's atmosphere from the standpoint of recent entry modeling techniques. The entry modeling has been carried out including a triggered progressive fragmentation model (TPFM) which maintains a maximum drag orientation for the fragments in either the collective or a non-collective wake limit during entry (ReVelle 2004). Specifically in this paper, we have proposed a new method of estimating the terminal bolide mass and have compared it against the corresponding single-body mass loss prediction. A new expression for the terminal mass is proposed that corrects the mass of the body for the changing mass to area ratio during the fragmentation process. As a result of this new work we have found two very interesting features that correspond very closely to those found from a direct analysis of the observational data. These include an instantaneous mass that closely resembles that directly observed and an ablation coefficient behavior that also strongly resembles meteor observations (such as those found recently by Ceplecha &amp; ReVelle 2005). During fragmentation, the apparent ablation coefficient has now been shown to decrease dramatically approaching the intrinsic ablation coefficient proposed by Ceplecha &amp; ReVelle (2005). In our modeling we have assumed a breakup into equal size fragments that are consistently and progressively multiples of two of the original unbroken leading piece. Had we assumed a multitude of many much smaller pieces that made up the totality of the original body, our predicted ablation coefficient would indeed have approached the very small intrinsic ablation parameter values predicted by Ceplecha and ReVelle. This is especially evident in the case of Sumava, but is also true in a number of other cases as well. The bolides whose properties have been modeled using our detailed entry code including a prediction of the panchromatic luminosity consist of the 1965 Revelstoke meteorite fall (Folinsbee 1967; Carr 1970; Shoemaker 1983), the 1974 Sumava fireball and the 1991 Benesov fireball as presented in Borovička &amp; Spurný (1996) and in Borovička et al. (1998), the Tagish Lake meteorite fall of January 8, 2000 (Brown et al. 2002), the March 9, 2002 Park Forest meteorite fall (Brown et al. 2004), the June 6, 2002 Mediterranean (Crete) bolide as presented in Brown et al. (2002) and finally the September 4, 2004 Antarctic bolide respectively (Klekociuk et al. 2005). A self-consistent assessment of the detailed properties of each of the fireballs was made using all available information for each event. In the future, more reliable estimates of all of the necessary source parameters (including their overall degree of bulk porosity) will be made if all channels of information are reliably retrieved for bolide events (channels such as acoustic-gravity waves and specifically its infrasound emission, seismic waves, satellite optical and IR data, ground-based spectroscopy, ground-based photometry and radiometry, VLF radiation, meteorite fragment recovery, etc.).

A microwave bridge, similar to the optical JAMIN interferometer, has been developed in order to determine the electron density in weakly ionized decaying plasmas. The discharge vessel was located in the open space between two horn antennas. A rather homogeneous excitation was accomplished by using an electrodeless high frequency (f = 13,6 MHz) discharge. Contrary to the common practice of using phase displacements several times of π, only very small displacements of the signal phase, traversing the plasma, have been used. The dimensions of the discharge vessel and the frequency of the microwave (f = 23 GHz; λ = 1,3 cm) have been properly chosen in order to have proportionality between the mean electron density and the oscilloscope trace. The range of electron-density investigated was about 108 to 1010 cm-3. The operation of the bridge has been investigated during the afterglow of a decaying nitrogen plasma. Simultaneous optical observations have shown that the intensity of the first negative bands of N2 + (B2Σu +-Χ2Σg +) is nearly proportional to the electron density. Using this correlation, the electron density profile across the discharge vessel has been evaluated. It could be shown that the time dependance of the electron density in the afterglow changes strongly within the discharge vessel. A comparison between the measurements of the electron density and the optical observations has shown that the microwave bridge is able to give some details of the electron density profile across the discharge vessel, inspite of the large wavelength used, compared with the dimensions of the discharge vessel.