The technique of transmission spectroscopy allows us to constrain the chemical composition of the atmospheres of transiting exoplanets. It relies on very high signal-to-noise spectroscopic (or ...spectrophotometric) observations and is thus most suited for bright exoplanet host stars. In the era of the Transiting Exoplanet Survey Satellite, Next Generation Space Telescope, and PLAnetary Transits and Oscillations of stars (PLATO), more and more suitable targets, even for mid-sized telescopes, are discovered. Furthermore, a wealth of archival data is available that could become a basis for long-term monitoring of exo-atmospheres. We analyzed archival High Accuracy Radial velocity Planet Searcher (HARPS) spectroscopic time series of four host stars to transiting bloated gas exoplanets, namely WASP-76b, WASP-127b, WASP-166b, and KELT-11b, searching for traces of sodium (sodium doublet), hydrogen (H , Hβ), and lithium (670.8 nm). The archival data sets include spectroscopic time series taken during transits. Comparing in- and out-of-transit spectra we can filter out the stellar lines and investigate the absorption from the planet. Simultaneously, the stellar activity is monitored using the Mg i and Ca i lines. We detect sodium in the atmosphere of WASP-76b at a 7-9 level. Furthermore, we report also at a 4-8 level of significance the detection of sodium in the atmosphere of WASP-127b, confirming earlier results based on low-resolution spectroscopy. The data show no sodium nor any other atom at high confidence levels for WASP-166b nor KELT-11b, hinting at the presence of thick high clouds.
Context.
WISE J085510.83−071442.5
(W0855) is a unique object: with
T
eff
≈ 250 K it is the coldest known brown dwarf (BD), located at only ≈2.2 pc form the Sun. It is extremely faint, which makes ...any astronomical observations difficult. However, at least one remotely similar ultra-low-mass object, the M9 dwarf
TVLM 513-46546
, has been shown to be a steady radio emitter at frequencies up to 95 GHz with superimposed active states where strong, pulsed emission is observed.
Aims.
Our goal is to determine the millimeter radio properties of W0855 with deep observations around 93 GHz (3.2 mm) in order to investigate whether radio astrometry of this object is feasible and to measure or set an upper limit on its magnetic field.
Methods.
We observed W0855 for 94 min at 85.1–100.9 GHz on 24 December 2019 using 44 of the Atacama Large millimeter Array (ALMA) 12 m antennas. We used the standard ALMA calibration procedure and created the final image for our analysis by accommodating the Quasar 3C 209, the brightest nearby object by far. Furthermore, we created a light curve with a 30 s time resolution to search for pulsed emission.
Results.
Our observations achieve a noise RMS of 7.3
μ
Jy beam
−1
for steady emission and of 88
μ
Jy for 30 s pulses in the aggregated bandwidth (Stokes
I
). There is no evidence for steady or pulsed emission from the object at the time of the observation. We derive 3
σ
upper limits of 21.9
μ
Jy on the steady emission and of 264
μ
Jy on the pulsed emission of W0855 between 85 GHz and 101 GHz.
Conclusions.
Together with the recent non-detection of W0855 at 4–8 GHz, our constraints on the steady and pulsed emission from W0855 confirm that the object is neither radio-loud nor magnetospherically particularly active.
ABSTRACT We present the results of a 15-yr long-term optical monitoring of 11 quasars conducted with the 2-m Ritchey–Chretien–Coude and the 50/70 cm Schmidt telescopes at the Rozhen National ...Astronomical Observatory, Bulgaria. Our observations are performed with standard Johnson-Cousins $VRI$ band filters and for each quasar we present a set of comparison standard stars that can be used for monitoring of objects in these fields (including finding charts for the stars identification). The variability and periodicity of each quasar are analysed individually and discussed. The physical properties of each quasar, such as their classification, redshift, and radio structures, are also discussed based on previous literature. Damped random walk model shows the best or the second best fit to the light curves of all objects. However, in six cases periodic models provide comparably good fits and make these six objects a valuable addition to the growing sample of quasars with periodic flux variation. They will be suitable for further investigation of the hitherto unclear mechanisms that give rise to this variability pattern. Our results provide important insights into the long-term variability and physical properties of quasars, which can further deepen our understanding of the nature and evolution of active galaxy nuclei.
ABSTRACT
We have derived high-spatial-resolution metallicity maps covering ∼105 deg2 across the Large Magellanic Cloud (LMC) using near-infrared passbands from the VISTA Survey of the Magellanic ...Clouds. We attempt to understand the metallicity distribution and gradients of the LMC up to a radius of ∼6 kpc. We identify red giant branch (RGB) stars in spatially distinct Y, (Y − Ks) colour–magnitude diagrams. In any of our selected subregions, the RGB slope is used as an indicator of the average metallicity, based on calibration to metallicity using spectroscopic data. The mean LMC metallicity is Fe/H = −0.42 dex (σFe/H = 0.04 dex). We find the bar to be mildly metal-rich compared with the outer disc, showing evidence of a shallow gradient in metallicity (−0.008 ± 0.001 dex kpc−1) from the galaxy’s centre to a radius of 6 kpc. Our results suggest that the LMC’s stellar bar is chemically similar to the bars found in large spiral galaxies. The LMC’s radial metallicity gradient is asymmetric. It is metal-poor and flatter towards the southwest, in the direction of the Bridge. This hints at mixing and/or distortion of the spatial metallicity distribution, presumably caused by tidal interactions between the Magellanic Clouds.
We analyse deep images from the VISTA survey of the Magellanic Clouds in the
$YJ{K_{\rm s}}$
filters, covering 14 deg2 (10 tiles), split into 120 subregions, and comprising the main body and Wing of ...the Small Magellanic Cloud (SMC). We apply a colour–magnitude diagram reconstruction method that returns their best-fitting star formation rate SFR(t), age–metallicity relation (AMR), distance and mean reddening, together with 68 per cent confidence intervals. The distance data can be approximated by a plane tilted in the East–West direction with a mean inclination of 39°, although deviations of up to ±3 kpc suggest a distorted and warped disc. After assigning to every observed star a probability of belonging to a given age–metallicity interval, we build high-resolution population maps. These dramatically reveal the flocculent nature of the young star-forming regions and the nearly smooth features traced by older stellar generations. They document the formation of the SMC Wing at ages <0.2 Gyr and the peak of star formation in the SMC Bar at ∼40 Myr. We clearly detect periods of enhanced star formation at 1.5 and 5 Gyr. The former is possibly related to a new feature found in the AMR, which suggests ingestion of metal-poor gas at ages slightly larger than 1 Gyr. The latter constitutes a major period of stellar mass formation. We confirm that the SFR(t) was moderately low at even older ages.
ABSTRACT
Reliable models of the thermally pulsing asymptotic giant branch (TP-AGB) phase are of critical importance across astrophysics, including our interpretation of the spectral energy ...distribution of galaxies, cosmic dust production, and enrichment of the interstellar medium. With the aim of improving sets of stellar isochrones that include a detailed description of the TP-AGB phase, we extend our recent calibration of the AGB population in the Small Magellanic Cloud (SMC) to the more metal-rich Large Magellanic Cloud (LMC). We model the LMC stellar populations with the trilegal code, using the spatially resolved star formation history derived from the VISTA survey. We characterize the efficiency of the third dredge-up by matching the star counts and the Ks-band luminosity functions of the AGB stars identified in the LMC. In line with previous findings, we confirm that, compared to the SMC, the third dredge-up in AGB stars of the LMC is somewhat less efficient, as a consequence of the higher metallicity. The predicted range of initial mass of C-rich stars is between Mi ≈ 1.7 and 3 M⊙ at Zi = 0.008. We show how the inclusion of new opacity data in the carbon star spectra will improve the performance of our models. We discuss the predicted lifetimes, integrated luminosities, and mass-loss rate distributions of the calibrated models. The results of our calibration are included in updated stellar isochrones publicly available.
ABSTRACT
We recover the spatially resolved star formation history across the entire main body and Wing of the Small Magellanic Cloud (SMC), using 14 deep tile images from the VISTA survey of the ...Magellanic Clouds (VMC) in the YJKs filters. The analysis is performed on 168 subregions of size 0.143 deg2 covering a total contiguous area of 23.57 deg2. We apply a colour–magnitude diagram (CMD) reconstruction method that returns the best-fitting star formation rate SFR(t), age–metallicity relation, distance and mean reddening, together with their confidence intervals, for each subregion. With respect to previous analyses, we use a far larger set of the VMC data, updated stellar models, and fit the two available CMDs (Y − Ks versus Ks and J − Ks versus Ks) independently. The results allow us to derive a more complete and more reliable picture of how the mean distances, extinction values, star formation rate, and metallicities vary across the SMC, and provide a better description of the populations that form its Bar and Wing. We conclude that the SMC has formed a total mass of (5.31 ± 0.05) × 108 M⊙ in stars over its lifetime. About two-thirds of this mass is expected to be still locked in stars and stellar remnants. 50 per cent of the mass was formed prior to an age of 6.3 Gyr, and 80 per cent was formed between 8 and 3.5 Gyr ago. We also illustrate the likely distribution of stellar ages and metallicities in different parts of the CMD, to aid the interpretation of data from future astrometric and spectroscopic surveys of the SMC.
Context. Interest in searches for extraterrestrial civilizations (ETCs) has been boosted in recent decades by the discovery of thousands of exoplanets. Aims. We turn to the classification of ETCs for ...new considerations that may help to design better strategies for searching for ETCs. Methods. This study is based on analogies with our own biological, historical, technological, and scientific development. We took a basic taxonomic approach to ETCs and investigated the implications of the new classification on ETC evolution and observational patterns. Finally, we used the quantitative scheme of Kardashev and considered its implications on the searches for ETCs as a counter example to our qualitative classification. Results. We propose a classification based on the abilities of ETCs to modify and integrate with their environments: Class 0 uses the environment as it is, Class 1 modifies the environment to fit its needs, Class 2 modifies itself to fit the environment, and a Class 3 ETC is fully integrated with the environment. Combined with the classical Kardashev scale, our scheme forms a two-dimensional method for interpreting ETC properties. Conclusions. The new framework makes it obvious that the available energy is not a unique measure of ETC progress: it may not even correlate with how well that energy is used. The possibility for progress without increased energy consumption implies a lower detectability, so in principle the existence of a Kardashev Type III ETC in the Milky Way cannot be ruled out. This reasoning weakens the Fermi paradox, allowing for the existence of advanced, yet not energy hungry, low-detectability ETCs. The integration of ETCs with the environment will make it impossible to tell technosignatures and natural phenomena apart. Therefore, the most likely opportunity for SETI searches to find advanced ETCs is to look for beacons, specifically set up by them for young civilizations like ours (if they would want to do that remains a matter of speculation). The other SETI window of opportunity is to search for ETCs at technological level similar to ours. To rephrase the famous saying of Arthur Clarke, sufficiently advanced civilizations are indistinguishable from nature.
In this paper we report a clustering analysis of upper main-sequence stars in the Small Magellanic Cloud, using data from the VMC survey (the VISTA near-infrared YJKs survey of the Magellanic ...system). Young stellar structures are identified as surface overdensities on a range of significance levels. They are found to be organized in a hierarchical pattern, such that larger structures at lower significance levels contain smaller ones at higher significance levels. They have very irregular morphologies, with a perimeter-area dimension of 1.44 0.02 for their projected boundaries. They have a power-law mass-size relation, power-law size/mass distributions, and a log-normal surface density distribution. We derive a projected fractal dimension of 1.48 0.03 from the mass-size relation, or of 1.4 0.1 from the size distribution, reflecting significant lumpiness of the young stellar structures. These properties are remarkably similar to those of a turbulent interstellar medium, supporting a scenario of hierarchical star formation regulated by supersonic turbulence.
EX Lupi, a low-mass young stellar object, went into an accretion-driven outburst in 2022 March. The outburst caused a sudden phase change of ∼112° ± 5° in periodically oscillating multiband ...lightcurves. Our high-resolution spectra obtained with the High Resolution Spectrograph (HRS) on board the Southern African Large Telescope also revealed a consistent phase change in the periodically varying radial velocities (RVs), along with an increase in the RV amplitude of various emission lines. The phase change and increase in RV amplitude morphologically translates to a change in the azimuthal and latitudinal location of the accretion hotspot over the stellar surface, which indicates a reconfiguration of the accretion funnel geometry. Our three-dimensional magnetohydrodynamic simulations reproduce the phase change for EX Lupi. To explain the observations, we explored the possibility of forward shifting of the dipolar accretion funnel as well as the possibility of the emergence of a new accretion funnel. During the outburst, we also found evidence of the hotspot’s morphology extending azimuthally asymmetrically with a leading hot edge and cold tail along the stellar rotation. Further, our high-cadence photometry showed that the accretion flow has clumps. We also detected possible clumpy accretion events in the HRS spectra that showed episodically highly blueshifted wings in the Ca ii IR triplet and Balmer H lines.
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