Search

A non-local-thermodynamic-equilibrium level population model of the first and second ionization stages of iron, nickel, and cobalt is used to fit a sample of XShooter optical + near-infrared (NIR) spectra of Type Ia supernovae (SNe Ia). From the ratio of the NIR lines to the optical lines limits can be placed on the temperature and density of the emission region. We find a similar evolution of these parameters across our sample. Using the evolution of the Fe  ii 12 570 –7155 Å  line as a prior in fits of spectra covering only the optical wavelengths we show that the 7200 Å  feature is fully explained by [Fe  ii ] and [Ni  ii ] alone. This approach allows us to determine the abundance of Ni  ii /Fe  ii for a large sample of 130 optical spectra of 58 SNe Ia with uncertainties small enough to distinguish between Chandrasekhar mass (M Ch) and sub-Chandrasekhar mass (sub- M Ch) explosion models. We conclude that the majority (85 per cent) of normal SNe Ia have a Ni/Fe abundance that is in agreement with predictions of sub- M Ch explosion simulations of ∼ Z ⊙ progenitors. Only a small fraction (11 per cent) of objects in the sample have a Ni/Fe abundance in agreement with M Ch explosion models. [ABSTRACT FROM AUTHOR]

The gigahertz peaked spectrum (GPS) sources, compact steep spectrum (CSS) radio sources, and high-frequency peaker (HFP) radio sources are thought to be young radio active galactic nuclei (AGNs) at the early stage of AGN evolution. We investigated the optical properties of the largest sample of 126 young radio AGNs based on the spectra in SDSS DR12. We find that the black hole masses M BH range from 107.32 to 109.84 |$\rm M_{\odot }$| and the Eddington ratios R edd vary from 10−4.93 to 100.37, suggesting that young radio AGNs have various accretion activities and not all are accreting at high accretion rate. Our young radio sources generally follow the evolutionary trend towards large-scale radio galaxies with increasing linear size and decreasing accretion rate in the radio power–linear size diagram. The radio properties of low-luminosity young radio AGNs with low R edd are discussed. The line width of [O  iii ] λ5007 core (σ[O  iii ]) is found to be a good surrogate of stellar velocity dispersion σ*. The radio luminosity |$L_{\rm 5\, GHz}$| correlates strongly with [O  iii ] core luminosity L [O  iii ], suggesting that radio activity and accretion are closely related in young radio sources. We find one object that can be defined as a narrow-line Seyfert 1 galaxy, representing a population of young AGNs with both young jet and early accretion activity. The optical variabilities of 15 quasars with multi-epoch spectroscopy were investigated. Our results show that the optical variability in young AGN quasars presents low variations (⁠|$\leqslant \! 60{{\ \rm per\ cent}}$|⁠) similar to the normal radio-quiet quasars. [ABSTRACT FROM AUTHOR]

Based on the cosmic shear data from the Canada–France–Hawaii Telescope Lensing Survey (CFHTLenS), Kilbinger et al. obtained a constraint on the amplitude of matter fluctuations of σ8(Ωm/0.27)0.6 = 0.79 ± 0.03 from the two-point correlation function (2PCF). This is ≈3σ lower than the value 0.89 ± 0.01 derived from Planck data on cosmic microwave background (CMB) anisotropies. On the other hand, based on the same CFHTLenS data, but using the power spectrum, and performing a different analysis, Liu et al. obtained the higher value of |$\sigma _8(\Omega _\mathrm{m}/0.27)^{0.64}=0.87^{+0.05}_{-0.06}$|⁠. We here investigate the origin of this difference, by performing a fair side-by-side comparison of the 2PCF and power spectrum analyses on CFHTLenS data. We find that these two statistics indeed deliver different results, even when applied to the same data in an otherwise identical procedure. We identify excess power in the data on small scales (ℓ > 5000) driving the larger values inferred from the power spectrum. We speculate on the possible origin of this excess small-scale power. More generally, our results highlight the utility of analysing the 2PCF and the power spectrum in tandem, to discover (and to help control) systematic errors. [ABSTRACT FROM AUTHOR]

We present Herschel Space Observatory Photodetector Array Camera and Spectrometer (PACS) and Spectral and Photometric Imaging Receiver Fourier Transform Spectrometer (SPIRE FTS) spectroscopy of a sample of 20 massive Young Stellar Objects (YSOs) in the Large and Small Magellanic Clouds (LMC and SMC). We analyse the brightest far-infrared (far-IR) emission lines, that diagnose the conditions of the heated gas in the YSO envelope and pinpoint their physical origin. We compare the properties of massive Magellanic and Galactic YSOs. We find that [O  i ] and [C  ii ] emission, that originates from the photo-dissociation region associated with the YSOs, is enhanced with respect to the dust continuum in the Magellanic sample. Furthermore the photoelectric heating efficiency is systematically higher for Magellanic YSOs, consistent with reduced grain charge in low metallicity environments. The observed CO emission is likely due to multiple shock components. The gas temperatures, derived from the analysis of CO rotational diagrams, are similar to Galactic estimates. This suggests a common origin to the observed CO excitation, from low-luminosity to massive YSOs, both in the Galaxy and the Magellanic Clouds. Bright far-IR line emission provides a mechanism to cool the YSO environment. We find that, even though [O  i ], CO, and [C  ii ] are the main line coolants, there is an indication that CO becomes less important at low metallicity, especially for the SMC sources. This is consistent with a reduction in CO abundance in environments where the dust is warmer due to reduced ultraviolet-shielding. Weak H2O and OH emission is detected, consistent with a modest role in the energy balance of wider massive YSO environments. [ABSTRACT FROM AUTHOR]

In this work, BVRI light curves of 55 Type II supernovae (SNe II) from the Lick Observatory Supernova Search programme obtained with the Katzman Automatic Imaging Telescope and the 1 m Nickel telescope from 2006 to 2018 are presented. Additionally, more than 150 spectra gathered with the 3 m Shane telescope are published. We conduct an analyse of the peak absolute magnitudes, decline rates, and time durations of different phases of the light and colour curves. Typically, our light curves are sampled with a median cadence of 5.5 d for a total of 5093 photometric points. In average, V -band plateau declines with a rate of 1.29 mag (100 d)−1, which is consistent with previously published samples. For each band, the plateau slope correlates with the plateau length and the absolute peak magnitude: SNe II with steeper decline have shorter plateau duration and are brighter. A time-evolution analysis of spectral lines in term of velocities and pseudo-equivalent widths is also presented in this paper. Our spectroscopic sample ranges between 1 and 200 d post-explosion and has a median ejecta expansion velocity at 50 d post-explosion of 6500 km s−1 (H α line) and a standard dispersion of 2000 km s−1. Nebular spectra are in good agreement with theoretical models using a progenitor star having a mass <16M⊙. All the data are available to the community and will help to understand SN II diversity better, and therefore to improve their utility as cosmological distance indicators. [ABSTRACT FROM AUTHOR]

The epoch corresponding to a redshift of z ∼ 6.5 is close to full re-ionization of the Universe, and early enough to provide an intriguing environment to observe the early stage of large-scale structure formation. It is also an epoch that can be used to verify the abundance of a large population of low luminosity star-forming galaxies that are deemed responsible for cosmic re-ionization. Here, we present the results of follow-up multi-object spectroscopy using OSIRIS at Gran Telescopio Canarias of 16 Ly α emitter (LAE) candidates discovered in the Subaru/XMM Newton Deep Survey. We have securely confirmed 10 LAEs with sufficient signal-to-noise ratio of the Ly α emission line. The inferred star formation rates of the confirmed LAEs are on the low side, within the range 0.9–4.7 M⊙ yr−1. However, they show relatively high Ly α rest frame equivalent widths. Finally we have shown that the mechanical energy released by the star formation episodes in these galaxies is enough to create holes in the neutral hydrogen medium such that Lyman continuum photons can escape to the intergalactic medium, thus contributing to the re-ionization of the Universe. [ABSTRACT FROM AUTHOR]

The object 4C 71.07 is a high-redshift blazar whose spectral energy distribution shows a prominent big blue bump and a strong Compton dominance. We present the results of a 2-yr multiwavelength campaign led by the Whole Earth Blazar Telescope (WEBT) to study both the quasar core and the beamed jet of this source. The WEBT data are complemented by ultraviolet and X-ray data from Swift , and by γ-ray data by Fermi. The big blue bump is modelled by using optical and near-infrared mean spectra obtained during the campaign, together with optical and ultraviolet quasar templates. We give prescriptions to correct the source photometry in the various bands for the thermal contribution, in order to derive the non-thermal jet flux. The role of the intergalactic medium absorption is analysed in both the ultraviolet and X-ray bands. We provide opacity values to deabsorb ultraviolet data, and derive a best-guess value for the hydrogen column density of |$N_{\rm H}^{\rm best}=6.3 \times 10^{20} \rm \, cm^{-2}$| through the analysis of X-ray spectra. We estimate the disc and jet bolometric luminosities, accretion rate, and black hole mass. Light curves do not show persistent correlations among flux changes at different frequencies. We study the polarimetric behaviour and find no correlation between polarization degree and flux, even when correcting for the dilution effect of the big blue bump. Similarly, wide rotations of the electric vector polarization angle do not seem to be connected with the source activity. [ABSTRACT FROM AUTHOR]

SALT spectra of the helium-rich hot subdwarf EC 22536−5304 show strong absorption lines of triply ionized lead. Analysis of the HRS spectrum and a follow-up SALT/RSS spectrum show EC 22536−5304 to have surface properties (temperature, gravity, helium/hydrogen ratio) similar to other heavy-metal subdwarfs. With a lead overabundance of 4.8 dex relative to solar, EC 22536−5304 is the most lead-rich intermediate helium subdwarf discovered so far. [ABSTRACT FROM AUTHOR]

We present the discovery of three new β Cep pulsators, three new pulsators with frequency groupings, and frequency patterns in a B3Ib star, all of which show pulsations with frequencies as high as about 17 d−1, with K2 space mission photometry. Based on a Fourier analysis and iterative pre-whitening, we present a classification and evaluate the potential for asteroseismic modelling. We include the lists of pulsation frequencies for three new β Cep pulsators, CD-28 12286, CD-27 10876, LS 3978, and additional pulsation mode frequencies for the known β Cep pulsator HD 164741. In addition, we characterize the regular frequency spacing found in the new pulsator HD 169173, and discuss its origin. We place the newly discovered variables in a colour–magnitude diagram using parallaxes from Gaia DR2 (second data release), showcasing their approximate location in the massive star domain. The identified frequency lists of these multiperiodic pulsators are a good starting point for future forward seismic modelling, after identification of at least one pulsation frequency from high-resolution time-series spectroscopy and/or multicolour photometry. [ABSTRACT FROM AUTHOR]

In the cold dark matter (CDM) picture of structure formation, galaxy mass distributions are predicted to have a considerable amount of structure on small scales. Strong gravitational lensing has proven to be a useful tool for studying this small-scale structure. Much of the attention has been given to detecting individual dark matter subhaloes through lens modelling, but recent work has suggested that the full population of subhaloes could be probed using a power spectrum analysis. In this paper, we quantify the power spectrum of small-scale structure in simulated galaxies, with the goal of understanding theoretical predictions and setting the stage for using measurements of the power spectrum to test dark matter models. We use a sample of simulated galaxies generated from the galacticus semi-analytic model to determine the power spectrum distribution first in the CDM paradigm and then in a warm dark matter scenario. We find that a measurement of the slope and amplitude of the power spectrum on galaxy strong lensing scales (k ∼ 1 kpc−1) could be used to distinguish between CDM and alternate dark matter models, especially if the most massive subhaloes can be directly detected via gravitational imaging. [ABSTRACT FROM AUTHOR]

Considerable uncertainties remain about the nature of warm, AGN-driven outflows and their impact on the evolution of galaxies. This is because the outflows are often unresolved in ground-based observations. As part of a project to study the AGN outflows in some of the most rapidly evolving galaxies in the local Universe, here we present Hubble Space Telescope (HST)/ Space Telescope Imaging Spectrograph (STIS) observations of F14394+5332E that resolve the sub-kpc warm outflow for the first time in an ultra-luminous infrared galaxy. The observations reveal a compact, high-ionization outflow region (r max ∼ 0.9 kpc) set in a more extensive (r max ∼ 1.4 kpc) halo that is kinematically quiescent and has a lower ionization state. A large line width (600 < FWHM < 1500 km s−1) is measured throughout the outflow region, and the outflowing gas shows a steep velocity gradient with radius, with the magnitude of the blueshifted velocities increasing from ∼500 to 1800 km s−1 from the inner to the outer part of the outflow. We interpret the observations in terms of the local acceleration, and hydrodynamic destruction, of dense clouds as they are swept up in a hot, low-density wind driven by the AGN. We discuss the implications for measuring the mass outflow rates and kinetic powers for the AGN-driven outflows in such objects. [ABSTRACT FROM AUTHOR]

MAXI J1813-095 is an X-ray transient discovered during an outburst in 2018. We report on X-ray and optical observations obtained during this event, which indicate that the source is a new low-mass X-ray binary. The outburst lasted ∼70 d and peaked at L X(0.5–10 keV) ∼ 7.6 × 1036 erg s−1, assuming a distance of 8 kpc. Swift /XRT follow-up covering the whole activity period shows that the X-ray emission was always dominated by a hard power-law component with a photon index in the range of 1.4–1.7. These values are consistent with MAXI J1813-095 being in the hard state, in agreement with the ∼30 per cent fractional root-mean-square amplitude of the fast variability (0.1–50 Hz) inferred from the only XMM–Newton observation available. The X-ray spectra are well described by a Comptonization emission component plus a soft, thermal component (kT ∼ 0.2 keV), which barely contributes to the total flux (≲8 per cent). The Comptonization y-parameter (∼1.5), together with the low temperature and small contribution of the soft component supports a black hole accretor. We also performed optical spectroscopy using the Very Large Telescope and Gran Telescopio Canarias telescopes during outburst and quiescence, respectively. In both cases, the spectrum lacks emission lines typical of X-ray binaries in outburst. Instead, we detect the Ca  ii triplet and H α in absorption. The absence of velocity shifts between the two epochs, as well as the evolution of the H α equivalent width, strongly suggest that the optical emission is dominated by an interloper, likely a G–K star. This favours a distance ≳3 kpc for the X-ray transient. [ABSTRACT FROM AUTHOR]

We present results from the analysis of high-resolution spectra obtained with the Keck HIRES spectrograph for a sample of 17 candidate extremely metal-poor (EMP) stars originally selected from commissioning data obtained with the SkyMapper telescope. Fourteen of the stars have not been observed previously at high dispersion. Three have [Fe/H] ≤ −3.0, while the remainder, with two more metal-rich exceptions, have −3.0 ≤ [Fe/H] ≤ −2.0 dex. Apart from Fe, we also derive abundances for the elements C, N, Na, Mg, Al, Si, Ca, Sc, Ti, Cr, Mn, Co, Ni, and Zn, and for n -capture elements Sr, Ba, and Eu. None of the current sample of stars is found to be carbon-rich. In general, our chemical abundances follow previous trends found in the literature, although we note that two of the most metal-poor stars show very low [Ba/Fe] (∼−1.7) coupled with low [Sr/Ba] (∼−0.3). Such stars are relatively rare in the Galactic halo. One further star, and possibly two others, meet the criteria for classification as a r -I star. This study, together with that of Jacobson et al. (2015), completes the outcomes of the SkyMapper commissioning data survey for EMP stars. [ABSTRACT FROM AUTHOR]

We use integral field spectroscopic (IFS) observations from Gemini Multi-Object Spectrograph-North (GMOS-N) to analyse the ionized gas in the principal star-forming region in the blue compact dwarf galaxy SBS 1415+437. The IFS data enable us to map the weak auroral line [O iii ] λ4363 at a spatial scale of ∼6.5 pc across a region of ∼143 × 143 pc2. This in turn allows us to use the robust direct T e-method to map the ionic and elemental abundances of nitrogen (N) along with the alpha-elements, oxygen (O), neon (Ne), sulphur (S), and argon (Ar). We utilize these abundances to map the relative abundances of N, Ne, S, and Ar with respect to O. We segment this pre-dominantly photoionized region of study into elliptical annuli on the basis of the H α flux distribution to study the variation of chemical abundances and their ratios, and find no significant chemical variation. We also perform chemical abundance analysis on the integrated spectra of the region under study and elliptical annuli within it. We find that the inferred abundances are in agreement with the median of the abundances obtained from the chemical abundance maps of the principal star-forming region and the mapped values within annuli. The finding has important implications for direct comparison with high-redshift observations, where spatial resolution is not available, and for a consistent approach to track chemical evolution across cosmic time. [ABSTRACT FROM AUTHOR]

We constrain cosmological parameters by analysing the angular power spectra of the Baryon Oscillation Spectroscopic Survey DR12 galaxies, a spectroscopic follow-up of around 1.3 million SDSS galaxies over 9376 deg2 with an effective volume of ∼6.5 (Gpc h −1)3 in the redshift range 0.15 ≤ |$z$| < 0.80. We split this sample into 13 tomographic bins (Δ |$z$|  = 0.05); angular power spectra were calculated using a Pseudo- C ℓ estimator, and covariance matrices were estimated using lognormal simulated maps. Cosmological constraints obtained from these data were combined with constraints from Planck cosmic microwave background experiment as well as the JLA supernovae compilation. Considering a |$w$| CDM cosmological model measured on scales up to k max = 0.07 h Mpc−1, we constrain a constant dark energy equation-of-state with an |${\sim } 4{{\ \rm per\ cent}}$| error at the 1σ level: |$w_0 = -0.993^{+0.046}_{-0.043}$|⁠, together with Ωm = 0.330 ± 0.012, Ωb = 0.0505 ± 0.002, |$S_8 \equiv \sigma _8 \sqrt{\Omega _\mathrm{ m}/0.3} = 0.863 \pm 0.016$|⁠, and h  = 0.661 ± 0.012. For the same combination of data sets, but now considering a ΛCDM (lambda cold dark matter) model with massive neutrinos and the same scale cut, we find Ωm = 0.328 ± 0.009, |$\Omega _\mathrm{ b} = 0.05017^{+0.0009}_{-0.0008}$|⁠, S 8 = 0.862 ± 0.017, and |$h = 0.663^{+0.006}_{-0.007}$|⁠, and a 95 per cent credible interval (CI) upper limit of ∑ m ν < 0.14 eV for a normal hierarchy. These results are competitive if not better than standard analyses with the same data set, and demonstrate that this should be a method of choice for future surveys, opening the door for their full exploitation in cross-correlation probes. [ABSTRACT FROM AUTHOR]

We research the requirements of high contrast imaging when combined with the cross-correlation (CC) of high-resolution spectra with known spectroscopic templates for detecting and characterizing exoplanets in reflected light. We simulate applying the technique to a potentially habitable Proxima b-like planet and show that the O2 A-band spectral feature could feasibly be detected on nearby rocky exoplanets using future instruments on the ELT. The technique is then more widely analysed showing that detections of planets and O2 with signal-to-noise ratio in the CC function (SNRCC) >3 can be obtained when the signal-to-noise ratio of the simulated planet spectrum (SNRspec) is from 0.25 to 1.2. We place constraints on the spectral resolution, instrument contrast, point spread function (PSF), exposure times and systematic error in stellar light subtraction for making such detections. We find that accurate stellar light subtraction (with 99.99 per cent removal) and PSFs with high spatial resolutions are key to making detections. Lastly a further investigation suggests the ELT could potentially discover and characterize planets of all sizes around different spectral type stars, as well as detecting O2 on super-Earths with habitable zone orbits around nearby M stars. [ABSTRACT FROM AUTHOR]

We investigate the implications of interference detection for experiments that are pursuing a detection of the redshifted 21-cm signals from the epoch of reionization (EoR). Interference detection causes samples to be sporadically flagged and rejected. As a necessity to reduce the data volume, flagged samples are typically (implicitly) interpolated during time or frequency averaging or uv-gridding. This so-far unexplored systematic biases of the 21-cm power spectrum, and it is important to understand this bias for current 21-cm experiments as well as the upcoming Square Kilometre Array EoR experiment. We analyse simulated data using power spectrum analysis and Gaussian process regression. We find that the combination of flagging and averaging causes tiny spectral fluctuations, resulting in 'flagging excess power'. This excess power does not substantially average down overtime and, without extra mitigation techniques, can exceed the power of realistic models of the 21-cm reionization signals in Low-Frequency Array (LOFAR) observations. We mitigate the bias by (i) implementing a novel way to average data using a Gaussian-weighted interpolation scheme, (ii) using unitary instead of inverse variance weighting of visibilities, and (iii) using low-resolution forward modelling of the data. After these modifications, which have been integrated in the LOFAR EoR processing pipeline, the excess power reduces by approximately three orders of magnitude, and is no longer preventing a detection of the 21-cm signals. [ABSTRACT FROM AUTHOR]

We present the latest results of our spectroscopic observations and refined modelling of a sample of detached eclipsing binaries, selected from the Kepler Eclipsing Binary Catalog, that are also double-lined spectroscopic binaries (SB2s). New high-resolution spectra obtained with the HIgh-Dispersion Echelle Spectrograph (HIDES), attached to the 1.88-m telescope of the Okayama Astrophysical Observatory, have supplemented the previous observations. This has allowed us to improve the physical parameters of some systems, and to characterize three previously omitted objects. All the obtained radial velocities were combined with Kepler photometry, in order to derive a full set of orbital and physical parameters. Ten out of eleven SB2s have their component spectra tomographically disentangled, and spectral analysis was performed with ispec, in order to derive the effective temperatures of components and the metallicities of the systems. By comparing our results with theoretical models, we assess the age and evolutionary status of the studied objects. We find a good match to all systems but one. We have derived distances from the parameters determined in this way, and we compare them with those from the Gaia Data Release 2. For systems previously studied by other authors, our new results lead to better consistency between observations and models. [ABSTRACT FROM AUTHOR]

This paper presents spectroscopic and seismic analyses of two rare hybrid pulsating subdwarf B (sdB) stars, PG 0048+091 and PG 1315−123, which are dominated by pressure (p)-mode pulsations. These are only the second and third sdB pulsators with detected frequency multiplets in both the p- and g (gravity)-mode regions. This allows an examination of the radial rotation profiles and p- and g-mode overtone spacings. Frequency multiplets indicate that PG 1315−123 rotates uniformly, as a solid body, while PG 0048+091 is rotating faster in the outer envelope. g- and p-mode overtone spacings for PG 1315−123 agree with previous findings and model predictions at 237 and ∼1000 s while those for PG 0048+091 are significantly shorter at 207 and <250 s, respectively. The cause of PG 0048+091's discrepancies is likely related to core structural differences which could be related to progenitor mass. Spectroscopic findings show that both stars lie on the hot end of the instability region and are most likely in long-period binaries with main-sequence companions. Their high temperatures challenge driving theory, which produces g-mode pulsations only at cooler temperatures. Another challenge is the appearance of pulsations with both driven and stochastic properties. Such a variety of pulsation properties makes these stars very interesting and important for understanding hot horizontal-branch stars. [ABSTRACT FROM AUTHOR]

21 cm power spectrum observations have the potential to revolutionize our understanding of the epoch of reionization and dark energy, but require extraordinarily precise data analysis methods to separate the cosmological signal from the astrophysical and instrumental contaminants. This analysis challenge has led to a diversity of proposed analyses, including delay spectra, imaging power spectra, m-mode analysis, and numerous others. This diversity of approach is a strength, but has also led to a confusion within the community about whether insights gleaned by one group are applicable to teams working in different analysis frameworks. In this paper, we show that all existing analysis proposals can be classified into two distinct families based on whether they estimate the power spectrum of the measured or reconstructed sky. This subtle difference in the statistical question posed largely determines the susceptibility of the analyses to foreground emission and calibration errors, and ultimately the science different analyses can pursue. In this paper, we detail the origin of the two analysis families, categorize the analyses being actively developed, and explore their relative sensitivities to foreground contamination and calibration errors. [ABSTRACT FROM AUTHOR]

We report on a comparison of spectroscopic analyses for hydrogen (DA) and helium atmosphere (DB) white dwarfs with Gaia Data Release 2 (DR2) parallaxes and photometry. We assume a reddening law and a mass–radius relation to connect the effective temperatures (T eff) and surface gravities (log  g) to masses and radii. This allows the comparison of two largely independent sets of fundamental parameters for 7039 DA and 521 DB stars with high-quality observations. This subset of the Gaia white dwarf sample is large enough to detect systematic trends in the derived parameters. We find that spectroscopic and photometric parameters generally agree within uncertainties when the expectation of a single star is verified. Gaia allows the identification of a small systematic offset in the temperature scale between the two techniques, as well as confirming a small residual high-mass bump in the DA mass distribution around 11 000–13 000 K. This assessment of the accuracy of white dwarf fundamental parameters derived from Gaia is a first step in understanding systematic effects in related astrophysical applications such as the derivation of the local stellar formation history, initial-to-final mass relation, and statistics of evolved planetary systems. [ABSTRACT FROM AUTHOR]

We present new spectroscopic data of the BL Lac RGB 2243 + 203, and its surroundings, obtained with the OSIRIS Multi Object Spectrograph (MOS) mounted in the Gran Telescopio Canarias (GTC). The spectra of neither the BL Lac nor its host galaxy show any spectral feature, thus hindering direct determination of its redshift. The spectroscopic redshift distribution of objects in the MOS field of view shows four galaxies with redshift between 0.5258 and 0.5288. We make use of a statistical analysis to test the possibility that the targeted BL Lac may be a member of that group. By using the spectroscopic redshifts obtained with our GTC observations, we found that this probability is between 86  and 93 per cent. [ABSTRACT FROM AUTHOR]

We report the discovery of VVV-WIT-07, a unique and intriguing variable source presenting a sequence of recurrent dips with a likely deep eclipse in 2012 July. The object was found serendipitously in the near-IR data obtained by the VISTA Variables in the Vía Láctea (VVV) ESO public survey. Our analysis is based on VVV variability, multicolour, and proper motion (PM) data. Complementary data from the VVV eXtended survey as well as archive data and spectroscopic follow-up observations aided in the analysis and interpretation of VVV-WIT-07. A search for periodicity in the VVV K s-band light curve of VVV-WIT-07 results in two tentative periods at P  ∼ 322 d and P  ∼ 170 d. Colours and PM are consistent either with a reddened main-sequence (MS) star or a pre-MS star in the foreground disc. The near-IR spectra of VVV-WIT-07 appear featureless, having no prominent lines in emission or absorption. Features found in the light curve of VVV-WIT-07 are similar to those seen in J1407 (Mamajek's object), a pre-MS K5 dwarf with a ring system eclipsing the star or, alternatively, to KIC 8462852 (Boyajian's star), an F3 IV/V star showing irregular and aperiodic dips in its light curve. Alternative scenarios, none of which is fully consistent with the available data, are also briefly discussed, including a young stellar object, a T Tauri star surrounded by clumpy dust structure, an MS star eclipsed by a nearby extended object, a self-eclipsing R CrB variable star, and even a long-period, high-inclination X-ray binary. [ABSTRACT FROM AUTHOR]

More than 100 galaxy-scale strong gravitational lens systems have been found by searching for the emission lines coming from galaxies with redshifts higher than the lens galaxies. Based on this spectroscopic-selection method, we introduce the deep Residual Networks (ResNet; a kind of deep Convolutional Neural Networks) to search for the galaxy-Ly  α emitter (LAE) lens candidates by recognizing the Ly  α emission lines coming from high- redshift galaxies (2 < |$z$| < 3) in the spectra of early-type galaxies (ETGs) at middle redshift (⁠|$z$| ∼ 0.5). The spectra of the ETGs come from the Data Release 12 (DR12) of the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey III (SDSS-III). In this paper, we first build a 28 layers ResNet model, and then artificially synthesize 150 000 training spectra, including 140 000 spectra without Ly  α lines and 10 000 ones with Ly  α lines, to train the networks. After 20 training epochs, we obtain a near-perfect test accuracy at 0.995 4. The corresponding loss is 0.002 8 and the completeness is 93.6 per cent. We finally apply our ResNet model to our predictive data with 174 known lens candidates. We obtain 1232 hits including 161 of the 174 known candidates (92.5 per cent discovery rate). Apart from the hits found in other works, our ResNet model also find 536 new hits. We then perform several subsequent selections on these 536 hits and present five most believable lens candidates. [ABSTRACT FROM AUTHOR]

We examine a magnitude limited (MB ≤ −18.7) sample of post-starburst (PSB) galaxies at 0.03 < |$z$| < 0.11 in the different environments from the spectroscopic data set of the Padova Millennium Galaxy Group Catalogue and compare their incidence and properties with those of passive (PAS) and emission line galaxies (EML). PSB galaxies have a quite precise lifetime (<1–1.5 Gyr), and they hold important clues for understanding galaxy evolution. While the properties (stellar mass, absolute magnitude, colour) of PSBs do not depend on environment, their frequency increases going from single galaxies to binary systems to groups, both considering the incidence with respect to the global number of galaxies and to the number of currently |$+$| recently star-forming galaxies. Including in our analysis, the sample of cluster PSBs drawn from the WIde-field Nearby Galaxy-cluster Survey presented in Paccagnella et al. we extend the halo mass range covered and present a coherent picture of the effect of the environment on galaxy transformations. We find that the PSB/(PSB  |$+$|  EML) fraction steadily increases with halo mass going from 1 per cent in |$10^{11} \, \mathrm{M}_{\odot}$| haloes to ∼15 per cent in the most massive haloes (⁠|$10^{15.5} \, \mathrm{M}_{\odot}$|⁠). This provides evidence that processes specific to the densest environments, such as ram-pressure stripping, are responsible for a large fraction of PSB galaxies in dense environments. These processes act on a larger fraction of galaxies than alternative processes leading to PSB galaxies in the sparsest environments, such as galaxy interactions. [ABSTRACT FROM AUTHOR]

We analysed RXTE/PCA observations of the bursting pulsar GRO J1744−28 during its two outbursts in 1995–1997. We have found a significant transition, i.e. a sharp change, of both spectral and timing properties around a flux of |$\rm 10^{-8}\ ergs\ cm^{-2}\ s^{-1}$| (3–30 keV), which corresponds to a luminosity of 2–8 |$\rm \times 10^{37}\ ergs\ s^{-1}$| for a distance of 4–8 kpc. We define the faint (bright) state when the flux is smaller (larger) than this threshold. In the faint state, the spectral hardness increases significantly with the increasing flux, while remaining almost constant in the bright state. In addition, we find that the pulsed fraction is positively related to both the flux and the energy (<30 keV) in both states. Due to the very stable pulse profile shape in all energy bands, a hard X-ray lag could be measured. This lag is only significant in the faint state (reaching ∼20 ms between 3–4 and 16–20 keV), and much smaller in the bright state (≲2 ms). We speculate that the discovered transition might be caused by changes of the accretion structure on the surface of the neutron star, and the hard X-ray lags are due to a geometry effect. [ABSTRACT FROM AUTHOR]

In the era of large-scale surveys of stars in the Milky Way, stellar ages are crucial for studying the evolution of the Galaxy. But determining ages of field stars is notoriously difficult; therefore, we attempt to determine benchmark ages for the extensively studied Gaia benchmark stars which can be used for validation purposes. By searching the literature for age estimates from different methods and deriving new ages based on Bayesian isochrone fitting, we are able to put reliable limits on the ages of 16 out of the 33 benchmark stars. The giants with well-defined ages are all young, and an expansion of the sample to include older giants with asteroseismic ages would be beneficial. Some of the stars have surface parameters inconsistent with isochrones younger than 16 Gyr. Including α-enhancement in the models when relevant resolves some of these cases, but others clearly highlight discrepancies between the models and observations. We test the impact of atomic diffusion on the age estimates by fitting to the actual surface metallicity of the models instead of the initial value and find that the effect is negligible except for a single turn-off star. Finally, we show that our ability to determine isochrone-based ages for large spectroscopic surveys largely mirrors our ability to determine ages for these benchmark stars, except for stars with log  g  ≳ 4.4 dex since their location in the Hertzsprung–Russell diagram is almost age insensitive. Hence, isochrone fitting does not constrain their ages given the typical uncertainties of spectroscopic stellar parameters. [ABSTRACT FROM AUTHOR]

H1743–322 is one of the few black hole candidates (BHCs) in low-mass X-ray binaries that shows mHz quasi-periodic oscillations (QPOs) that are not associated with the more common type A, B, and C oscillations seen in the X-ray light curves of typical BHC systems. To better understand the physical origin of the mHz oscillations, we carried out a phase-resolved spectroscopic study of two RXTE observations of this source. As previously reported, the averaged energy spectra of H1743–322 show a strong iron line at ∼6.5 keV. Here we found evidence that the line flux appears to be modulated at twice the frequency of the mHz QPO. This line flux modulation is very similar to the one previously found for the type-C QPO in this source. We interpret the possibly periodic line flux modulation with this mHz QPO in terms of Lense–Thirring precession of the inner flow, and discuss the possible connection with the modulation of the line properties with the type-C QPO frequency. [ABSTRACT FROM AUTHOR]

The environmental dependence of galaxy clustering encodes information about the physical processes governing the growth of cosmic structure. We analyse the baryon acoustic peak as a function of environment in the galaxy correlation function of the Baryon Oscillation Spectroscopic Survey CMASS sample. Dividing the sample into three sub-sets by smoothed local overdensity, we detect acoustic peaks in the six separate autocorrelation and cross-correlation functions of the sub-samples. Fitting models to these correlation functions, calibrated by mock galaxy and dark matter catalogues, we find that the inferred distance scale is independent of environment, and consistent with the result of analysing the combined sample. The shape of the baryon acoustic feature, and the accuracy of density-field reconstruction in the Zeldovich approximation, varies with environment. By up-weighting underdense regions and down-weighting overdense regions in their contribution to the full-sample correlation function, by up to |$50{{\ \rm per\ cent}}$|⁠, we achieve a fractional improvement of a few per cent in the precision of baryon acoustic oscillation fits to the CMASS data and mock catalogues: the scatter in the preferred-scale fits to the ensemble of mocks improves from |$1.45{{\ \rm per\ cent}}$| to |$1.34{{\ \rm per\ cent}}$| (pre-reconstruction) and |$1.03{{\ \rm per\ cent}}$| to |$1.00{{\ \rm per\ cent}}$| (post-reconstruction). These results are consistent with the notion that the acoustic peak is sharper in underdense environments. [ABSTRACT FROM AUTHOR]

Transmission spectroscopy of exoplanets has the potential to provide precise measurements of atmospheric chemical abundances, in particular of hot Jupiters whose large sizes and high temperatures make them conducive to such observations. To date, several transmission spectra of hot Jupiters have revealed low amplitude features of water vapour compared to expectations from cloud-free atmospheres of solar metallicity. The low spectral amplitudes in such atmospheres could either be due to the presence of aerosols that obscure part of the atmosphere or due to inherently low abundances of H2O in the atmospheres. A recent survey of transmission spectra of ten hot Jupiters used empirical metrics to suggest atmospheres with a range of cloud/haze properties but with no evidence for H2O depletion. Here, we conduct a detailed and homogeneous atmospheric retrieval analysis of the entire sample and report the H2O abundances, cloud properties, terminator temperature profiles, and detection significances of the chemical species. This study finds that the majority of hot Jupiters have atmospheres consistent with subsolar H2O abundances at their day–night terminators. The best constrained abundances range from log(H2O) of |$-5.04^{+0.46}_{-0.30}$| to |$-3.16^{+0.66}_{-0.69}$|⁠, which compared to expectations from solar-abundance equilibrium chemistry correspond to |$0.018^{+0.035}_{-0.009}\times$| solar to |$1.40^{+4.97}_{-1.11}\times$| solar. Besides H2O we report statistical constraints on other chemical species and cloud/haze properties, including cloud/haze coverage fractions which range from |$0.18^{+0.26}_{-0.12}$| to |$0.76^{+0.13}_{-0.15}$|⁠. The retrieved H2O abundances suggest subsolar oxygen and/or supersolar C/O ratios, and can provide important constraints on the formation and migration pathways of hot giant exoplanets. [ABSTRACT FROM AUTHOR]

We report results from a broad-band spectral analysis of the low mass X-ray binary MXB 1658–298 with the Swift /X-Ray Telescope and Nuclear Spectroscopic Telescope Array (NuSTAR) observations made during its 2015–2017 outburst. The source showed different spectral states and accretion rates during this outburst. The source was in low/hard state during 2015; and it was in high/soft state during the 2016 NuSTAR observations. This is the first time that a comparison of the soft and hard spectral states during an outburst is being reported in MXB 1658–298. Compared with the observation of 2015, the X-ray luminosity was about four times higher during 2016. The hard state spectrum can be well described with models consisting of a single-temperature blackbody component along with Comptonized disc emission, or three-component model comprising multicolour disc, single-temperature blackbody, and thermal Comptonization components. The soft state spectrum can be described with blackbody or disc blackbody and Comptonization component, where the neutron star surface (or boundary layer) is the dominant source for the Comptonization seed photons. We have also found a link between the spectral state of the source and the Fe K absorber. The absorption features due to highly ionized Fe were observed only in the soft state. This suggests a probable connection between accretion disc wind (or atmosphere) and spectral state (or accretion state) of MXB 1658–298. [ABSTRACT FROM AUTHOR]

Massive companions in close orbits around G dwarfs are thought to undergo rapid orbital decay due to runaway tidal dissipation. We report here the discovery of WASP-128b, a brown dwarf discovered by the WASP survey transiting a G0V host on a |$2.2\, \mathrm{d}$| orbit, where the measured stellar rotation rate places the companion in a regime where tidal interaction is dominated by dynamical tides. Under the assumption of dynamical equilibrium, we derive a value of the stellar tidal quality factor |$\log {Q_\star ^{\prime }} = 6.96 \pm 0.19$|⁠. A combined analysis of ground-based photometry and high-resolution spectroscopy reveals a mass and radius of the host, |$M_\star = 1.16\pm 0.04\, \mathrm{M}_{\odot }$|⁠, |$R_\star = 1.16\pm 0.02\, \mathrm{R}_{\odot }$|⁠, and for the companion, |$M_\mathrm{b} = 37.5\pm 0.8\, M_\mathrm{J}$|⁠, |$R_\mathrm{b} = 0.94\pm 0.02\, R_\mathrm{J}$|⁠, placing WASP-128b in the driest parts of the brown dwarf desert, and suggesting a mild inflation for its age. We estimate a remaining lifetime for WASP-128b similar to that of some ultra-short period massive hot Jupiters, and note it may be a propitious candidate for measuring orbital decay and testing tidal theories. [ABSTRACT FROM AUTHOR]

We study projected underdensities in the cosmic galaxy density field known as 'troughs', and their overdense counterparts, which we call 'ridges'. We identify these regions using a bright sample of foreground galaxies from the photometric Kilo-Degree Survey (KiDS), specifically selected to mimic the spectroscopic Galaxy And Mass Assembly survey. Using background galaxies from KiDS, we measure the weak gravitational lensing profiles of the troughs/ridges. We quantify the amplitude of their lensing strength A as a function of galaxy density percentile rank P and galaxy overdensity δ, and find that the skewness in the galaxy density distribution is reflected in the total mass distribution measured by weak lensing. We interpret our results using the mock galaxy catalogue from the Marenostrum Institut de Ciències de l'Espai (MICE) simulation, and find a good agreement with our observations. Using signal-to-noise weights derived from the Scinet LIghtCone Simulations (SLICS) mock catalogue we optimally stack the lensing signal of KiDS troughs with an angular radius |$\theta _{\rm A} = \lbrace 5,10,15,20\rbrace \, {\rm arcmin}$|⁠, resulting in |$\lbrace 16.8,14.9,10.13,7.55\rbrace \, \sigma$| detections. Finally, we select troughs using a volume-limited sample of galaxies, split into two redshift bins between 0.1 < |$z$| < 0.3. For troughs/ridges with transverse comoving radius |$R_{\rm A}=1.9\, h_{70}^{-1}\, {\rm {Mpc}}$|⁠, we find no significant difference in the comoving excess surface density as a function of P and δ between the low- and high-redshift sample. Using the MICE and SLICS mocks we predict that trough and ridge evolution could be detected with gravitational lensing using deeper and wider lensing surveys, such as those from the Large Synoptic Survey Telescope and Euclid. [ABSTRACT FROM AUTHOR]

Magnetic reconnection is invoked as an efficient particle accelerator in a variety of astrophysical sources of non-thermal high-energy radiation. With large-scale two-dimensional particle-in-cell simulations of relativistic reconnection (i.e. with magnetization σ ≫ 1) in pair plasmas, we study the long-term evolution of the power-law slope and high-energy cut-off of the spectrum of accelerated particles. We find that the high-energy spectral cut-off does not saturate at γcut∼ 4σ, as claimed by earlier studies, but it steadily grows with time as long as the reconnection process stays active. At late times, the cut-off scales approximately as |$\gamma _{\rm cut}\propto \sqrt{t}$|⁠, regardless of the flow magnetization and initial temperature. We show that the particles dominating the high-energy spectral cut-off reside in plasmoids, and in particular in a strongly magnetized ring around the plasmoid core. The growth of their energy is driven by the increase in the local field strength, coupled with the conservation of the first adiabatic invariant. We also find that the power-law slope of the spectrum (p = −d log N /d log γ) evolves with time. For σ ≳ 10, the spectrum is hard at early times (p ≲ 2), but it tends to asymptote to p ∼ 2; the steepening of the power-law slope allows the spectral cut-off to extend to higher and higher energies, without violating the fixed energy budget of the system. Our results demonstrate that relativistic reconnection is a viable candidate for accelerating the high-energy particles emitting in relativistic astrophysical sources. [ABSTRACT FROM AUTHOR]

We report the discovery of rapid variations of a high-velocity Mg ii broad absorption line (BAL) trough in the quasar SDSS J133356.02 + 001229.1 (⁠|$z$| em∼ 0.9197). Vivek et al. revealed the emergence and subsequent near disappearance of a BAL component in this source having an ejection velocity of ∼28 000  km s−1. Our further follow-up studies with South African Large Telescope (SALT) reveal the dramatic nature of the absorption line variability in this source. The absorption line emerged again at the same velocity and nearly disappeared within the SALT observations. Our observations allow us to probe variability over time-scales of the order of few days to 4.2 yr in the QSO rest frame. The observed velocity stability of BAL absorption does not point to any line-of-sight acceleration/deceleration of BAL clouds. The ionization parameter of the absorbing cloud is constrained from the column density ratio of Mg ii to Fe ii ground state absorption. In the absence of strong optical continuum variability, we suggest that photoionization-driven BAL variability due to changes in the shielding, multiple streaming clouds across our line of sight in a corotating wind, or a combination of both as possible explanations for the observed strong equivalent width variations. [ABSTRACT FROM AUTHOR]

We present results from an ongoing investigation using the Kilo Degree Survey (KiDS) on the VLT Survey Telescope (VST) to provide a census of ultra-compact massive galaxies (UCMGs), defined as galaxies with stellar masses |${M_{\star }}\gt 8 \times 10^{10} \, \rm {\mathrm{ M}_\odot}$| and effective radii |${R_{\rm e}}\lt 1.5\, \rm kpc$|⁠. UCMGs, which are expected to have undergone very few merger events, provide a unique view on the accretion history of the most massive galaxies in the Universe. Over an effective sky area of nearly 330 deg2, we select UCMG candidates from KiDS multicolour images, which provide high quality structural parameters, photometric redshifts, and stellar masses. Our sample of ∼1000 photometrically selected UCMGs at |$z$| < 0.5 represents the largest sample of UCMG candidates assembled to date over the largest sky area. In this paper, we present the first effort to obtain their redshifts using different facilities, starting with first results for 28 candidates with redshifts |$z$| < 0.5, obtained at NTT and TNG telescopes. We confirmed, as bona fide UCMGs, 19 out of the 28 candidates with new redshifts. A further 46 UCMG candidates are confirmed with literature spectroscopic redshifts (35 at |$z$| < 0.5), bringing the final cumulative sample of spectroscopically confirmed lower- z UCMGs to 54 galaxies, which is the largest sample at redshifts below 0.5. We use these spectroscopic redshifts to quantify systematic errors in our photometric selection, and use these to correct our UCMG number counts. We finally compare the results to independent data sets and simulations. [ABSTRACT FROM AUTHOR]

We consider an alternative to the cross-correlation function (CCF), which uses the autocorrelation function (ACF), to measure in spectra the reflected light of the stars by their planetary companion. The objective of this work is to assess and analyse the efficiency of the ACF in detecting planetary signals by a detection of reflected light. To do so, we first compare the ACF and the CCF using artificial spectra containing a planetary signal. We then use the ACF to analyse spectra of the 51 Peg |$+$| 51 Peg b system and compare our results with those obtained by Martins et al. who previously analysed the same system using the CCF. The functionalities of the ACF and the way it is implemented are similar to that of the CCF. One of the main advantages of the ACF is the fact that, unlike the CCF, no weighted binary mask is required. This makes the ACF easier to use. The results related to simulated spectra showed that the ACF allowed us to decrease the boundary condition threshold for the use of spectra compared to the CCF so that more data could be used to recover the planetary signal. For the 51 Peg b planet, we achieved a detection significance of 5.52 σnoisewith the ACF compared to 3.70 σnoisewith the CCF. We conclude that the ACF has the potential to become a prominent technique in detecting exoplanets considering its efficiency, ease of use, and rapid execution time. [ABSTRACT FROM AUTHOR]

We determine the properties of the binary star V106 in the old open cluster NGC 6791 . We identify the system to be a blue straggler cluster member by using a combination of ground-based and Kepler photometry and multi-epoch spectroscopy. The properties of the primary component are found to be |$M_{\rm p}\sim 1.67\, \rm M_{\odot }$|⁠, more massive than the cluster turn-off, with |$R_{\rm p}\sim 1.91\, \rm R_{\odot }$| and T eff= 7110 ± 100 K. The secondary component is highly oversized and overluminous for its low mass with |$M_{\rm s}\sim 0.182\, \rm M_{\odot }$|⁠, |$R_{\rm s}\sim 0.864\, \rm R_{\odot }$|⁠, and T eff= 6875 ± 200 K. We identify this secondary star as a bloated (proto) extremely low-mass helium white dwarf. These properties of V106 suggest that it represents a typical Algol-paradox system and that it evolved through a mass-transfer phase, which provides insight into its past evolution. We present a detailed binary stellar evolution model for the formation of V106 using the mesa code and find that the mass-transfer phase only ceased about |$40\, {\rm Myr}$| ago. Due to the short orbital period (P = 1.4463 d), another mass-transfer phase is unavoidable once the current primary star evolves towards the red giant phase. We argue that V106 will evolve through a common-envelope phase within the next |$100\, {\rm Myr}$| and merge to become a single overmassive giant. The high mass will make it appear young for its true age, which is revealed by the cluster properties. Therefore, V106 is potentially a prototype progenitor of old field giants masquerading as young. [ABSTRACT FROM AUTHOR]

We present a study of seven southern open clusters based on UBVRI CCD photometry (Johnsons-Cousins system) and Gaia DR2 data. Dias 4, Dias 6, and four other clusters had UBVRI photometric observations determined for the first time. From the observational UBVRI data we obtained photometric membership probability estimates and, using the proper motions from the UCAC5 catalogue, we also determined the kinematic membership. From Gaia DR2 astrometric data we determine the stellar membership using proper motions and parallaxes, taking into account the full covariance matrix. For both independent sets of data and membership we apply our non-subjective multidimensional global optimization tool to fit theoretical isochrones to determine the distance, age, reddening, metallicity, and binary fraction of the clusters. The results of the mean proper motions, distances, and ages are in agreement, but the ones obtained from Gaia DR2 data are more precise in both membership selection and estimated parameters. In the case of NGC 6087, the Cepheid S Nor, member of the open cluster, was used to obtain an independent distance estimate, confirming the one determined by our fitting method. We also report a serendipitous discovery of two new clusters in the extended field near what was originally Dias 4. [ABSTRACT FROM AUTHOR]

X-ray variability of accreting black hole binaries is believed to be produced by the fluctuations propagating towards the compact object. Observations suggest the light curves in different energy bands are connected, but the fluctuations at harder energies are delayed with respect to the softer ones. The standard interpretation involves dependence of the X-ray spectral hardness on the radial distance, with harder spectra emitted closer to the black hole. Recently, a number of challenges to this scenario have been found, both at qualitative and quantitative level. The model does not predict the large magnitude of the delay between different energies, as well as the dependence of variability amplitude on the spectral range and frequency. We study timing properties of accreting black hole X-ray binaries taking into account peculiarities of spectral formation in these sources. We show that the simultaneous presence of two components leads to a complex shape of power spectra and phase lags between the X-ray bands: the amplitude of the phase lag becomes independent of the delay between the components, and the power spectra show an artificial decrease or, on the contrary, enhancement of power at low Fourier frequencies. This provides an essential ingredient for the reinstatement of the propagating fluctuations model. The work draws attention to the importance of considering conditions of spectral formation when studying timing properties. [ABSTRACT FROM AUTHOR]

We describe here a novel design of a fast high-density robotized fiber positioner system for massive spectroscopic surveys. The fiber positioners are compact, robust, and they can be coordinated, allowing for a high spatial density. Furthermore, the high absolute accuracy removes the need for a metrology system and reduces the reconfiguration time. First, we present the requirements for such a high-density fiber positioner system and put them in relation with the science goals. Then, we discuss the positioner design that accomplishes these requirements (including mechanical design, local control electronics board, overall communication solution, and observation sequencing). Finally, the performance of the proposed design is measured using 25 mm pitch prototypes of the positioners, through a dedicated novel designed test-bench. The related results show that our prototypes fulfil the requirements particularly in terms of positioning precision (<20 µm rms for one single open loop move) and partially in tilt (<0.15 deg). [ABSTRACT FROM AUTHOR]

Transmission spectroscopy provides a powerful probe of the atmospheric properties of transiting exoplanets. To date, studies of exoplanets in transit have focused on inferring their atmospheric properties such as chemical compositions, cloud/haze properties, and temperature structures. However, surface inhomogeneities in the host stars of exoplanets in the form of cool spots and hot faculae can in principle imprint signatures on the observed planetary transit spectrum. Here we present Aura, a new retrieval paradigm for inferring both planetary and stellar properties from a transmission spectrum. We apply our retrieval framework to a sample of hot giant exoplanets to determine the significance of stellar heterogeneity and clouds/hazes in their spectra. The retrieval analyses distinguish four groups of planets. First, the spectra of WASP-6b and WASP-39b are best characterized by imprints of stellar heterogeneity and hazes and/or clouds. HD 209458b and HAT-P-12b comprise the second group for which there is weak evidence for stellar heterogeneity and a high significance of hazes and/or clouds. The third group constitutes HAT-P-1b and WASP-31b and shows weak evidence against stellar heterogeneity but weak to substantial indications of clouds/hazes. The fourth group – WASP-19b, WASP-17b, and WASP-12b – is fit best by molecular and alkali absorbers with H2 scattering without evidence for stellar heterogeneity and weak to no evidence for clouds/hazes. Our retrieval methodology paves the way to simultaneous information on the star and planet from higher resolution spectra using future facilities such as the James Webb Space Telescope and large ground-based facilities. [ABSTRACT FROM AUTHOR]

We present the 1–100 GeV spectral energy distribution (SED) for a population of 148 high-synchrotron-peaked (HSP) blazars recently detected with Fermi -LAT as part of the First Brazil-ICRANet Gamma-ray Blazar (1BIGB) catalogue. Most of the 1BIGB sources have their γ-ray spectral properties presented here for the first time, representing a significant new extension of the γ-ray blazar population. Since our sample was originally selected from an excess signal in the 0.3–500 GeV band, the sources stand out as promising TeV blazar candidates, potentially in reach of the forthcoming very high energy (VHE) γ-ray observatory, Cherenkov Telescope Array (CTA). The flux estimates presented here are derived considering PASS8 data, integrating over more than 9 yr of Fermi -LAT observations. We also review the full broad-band fit between 0.3 and 500 GeV presented in the original 1BIGB paper for all sources, updating the power-law parameters with currently available Fermi -LAT data set. The importance of these sources in the context of VHE population studies with both current instruments and the future CTA is evaluated. To do so, we select a subsample of 1BIGB sources and extrapolate their γ-ray SEDs to the highest energies, properly accounting for absorption due to the extragalactic background light. We compare those extrapolations to the published CTA sensitivity curves and estimate their detectability by CTA. Two notable sources from our sample, namely 1BIGB J224910.6 − 130002 and 1BIGB J194356.2+211821, are discussed in greater detail. All γ-ray SEDs are made publicly available via the Brazilian Science Data Center (BSDC) service, maintained at CBPF, in Rio de Janeiro. [ABSTRACT FROM AUTHOR]

We present the study of the dynamical status of the galaxy cluster CL1821+643, a rare and intriguing cool-core cluster hosting a giant radio halo. We base our analysis on new spectroscopic data for 129 galaxies acquired at the Italian Telescopio Nazionale Galileo. We also use spectroscopic data available from the literature and photometric data from the Sloan Digital Sky Survey. We select 120 cluster member galaxies and compute the cluster redshift 〈 $$z$$ 〉 ∼ 0.296 and the global line-of-sight velocity dispersion σV ∼ 1100 km s−1. The results of our analysis are consistent with CL1821+643 being a massive (M > 1015 M⊙) dynamically relaxed cluster dominated by a big and luminous elliptical at the centre of the cluster potential well. None of the tests employed to study the cluster galaxies kinematics in the 1D (velocity information), 2D (spatial information), and 3D (combined velocity and spatial information) domains is able to detect significant substructures. While this picture is in agreement with previous results based on X-ray data and on the existence of the central cool core, we do not find any evidence of a merging process responsible for the radio halo discovered in this cluster. Thus, this radio halo remains an open problem that raises doubts about our understanding of diffuse radio sources in clusters. [ABSTRACT FROM AUTHOR]

We present in this paper new electron impact widths for 12 Ar  v and 22 Ar vi lines. Neither experimental nor theoretical results have been found for these ions to perform comparisons. The results have been obtained using our quantum mechanical method. Results are presented for an electron density N e = 1018 cm−3 and at a large range of electron temperatures (2 × 104–106 K) required for plasma modelling. The atomic structure and collision data used for the calculations of line broadening are also calculated by our codes. We use our calculated widths to fit a dependence on electron temperature. We check that the obtained relation is valid for all the studied lines. The present results are required for many applications, especially for accurate spectroscopic diagnostics and modelling in astrophysics and in tokamaks, laboratory plasma physics, and technological plasmas. [ABSTRACT FROM AUTHOR]

We use the DECaLS DR3 survey photometry matched to the SDSS-III/BOSS DR12 spectroscopic catalogue to investigate the morphology and stellar mass–size relation of luminous red galaxies within the CMASS and LOWZ galaxy samples in the redshift range 0.2 < $$z$$ < 0.7. The large majority of both samples is composed of early-type galaxies with De Vaucouleurs profiles, while only less than 20 per cent are late-type exponentials. We calibrate DECaLS effective radii using the higher-resolution CFHT/MegaCam observations and optimize the correction for each morphological type. By cross-matching the photometric properties of the early-type population with the Portsmouth stellar mass catalogue, we are able to explore the high-mass end of the distribution using a large sample of 322994 galaxies over 4380 deg2. We find a clear correlation between the sizes and stellar masses of these galaxies, which appears flatter than previous estimates at lower masses. The sizes of these early-type galaxies do not exhibit significant evolution within the BOSS redshift range, but a slightly declining redshift trend is found when these results are combined with $$z$$ ∼ 0.1 SDSS measurements at the high-mass end. The synergy between BOSS and DECaLS has important applications in other fields, including galaxy clustering and weak lensing. [ABSTRACT FROM AUTHOR]

New methods have recently been developed to search for strong gravitational lenses, in particular lensed quasars, in wide-field imaging surveys. Here, we compare the performance of three different, morphology- and photometry-based methods to find lens candidates within the Kilo-Degree Survey (KiDS) DR3 footprint (440 deg2). The three methods are: i) a multiplet detection in KiDS-DR3 and/or Gaia-DR1, ii) direct modelling of KiDS cutouts, and iii) positional offsets between different surveys (KiDS-versus-Gaia, Gaia-versus-2MASS), with purpose-built astrometric recalibrations. The first benchmark for the methods has been set by the recovery of known lenses. We are able to recover seven out of 10 known lenses and pairs of quasars observed in the KiDS DR3 footprint, or eight out of 10 with improved selection criteria and looser colour pre-selection. This success rate reflects the combination of all methods together, which, taken individually, performed significantly worse (four lenses each). One novelty of our analysis is that the comparison of the performances of the different methods has revealed the strengths and weaknesses of the approaches and, most of all, the complementarity. We finally provide a list of high-grade candidates found by one or more methods, awaiting spectroscopic follow-up for confirmation. Of these, KiDS 1042+0023 is, to our knowledge, the first confirmed lensed quasar from KiDS, exhibiting two quasar spectra at the same source redshift at either sides of a red galaxy, with uniform flux-ratio f ≈ 1.25 over the wavelength range $$0.45\, \mu \mathrm{m}\lt \lambda \lt 0.75\, \mu \mathrm{m}.$$ [ABSTRACT FROM AUTHOR]

SBS 0335 − 052E, one of the most metal-poor (Z ∼ 3–4 $${{\ \rm per\ cent}}$$ Z⊙) He  ii -emitter starbursts known in the nearby Universe, is studied using optical VLT/MUSE spectroscopic and Chandra X-ray observations. We spatially resolved the spectral map of the nebular He  ii λ4686 emission from which we derived for the first time the total He  ii -ionizing energy budget of SBS 0335 − 052E. The nebular He  ii line is indicative of a quite hard ionizing spectrum with photon energies > 4 Ryd, and is observed to be more common at high- $$z$$ than locally. Our study rules out a significant contribution from X-ray sources and shocks to the He  ii photoionization budget, indicating that the He+ excitation is mainly due to hot stellar continua. We discovered a new WR knot, but we also discard single Wolf–Rayet stars as the main responsible for the He  ii ionization. By comparing observations with current models, we found that the He  ii -ionization budget of SBS 0335 − 052E can only be produced by either single, rotating metal-free stars or a binary population with Z ∼ 10−5 and a 'top-heavy' initial mass function. This discrepancy between the metallicity of such stars and that of the H  ii regions in SBS 0335 − 052E is similar to results obtained by Kehrig et al. for the very metal-deficient He  ii -emitting galaxy IZw18. These results suggest that the He  ii ionization is still beyond the capabilities of state-of-the-art models. Extremely metal-poor, high-ionizing starbursts in the local Universe, like SBS 0335 − 052E, provide unique laboratories for exploring in detail the extreme conditions likely prevailing in the reionization era. [ABSTRACT FROM AUTHOR]

We discovered two bright DO-type white dwarfs, GALEX J053628.3+544854 (J0536+5448) and GALEX J231128.0+292935(J2311+2929), which rank among the eight brightest DO-type white dwarfs known. Our non-LTE model atmosphere analysis reveals effective temperatures and surface gravities of $${T_\mathrm{eff}}\, = 80000\pm 4600 \, \mathrm{K}$$ and $$\log g = 8.25\pm 0.15$$ for J0536+5448 and $${T_\mathrm{eff}}\, = 69400\pm 900 \, \mathrm{K}$$ and $$\log g = 7.80\pm 0.06$$ for J2311+2929. The latter shows a significant amount of carbon in its atmosphere ($$C=0.003^{+0.005}_{-0.002}$$, by mass), while for J0536+5448 we could derive only an upper limit of C  < 0.003. Furthermore, we calculated spectroscopic distances for the two stars and found a good agreement with the distances derived from the Gaia parallaxes. [ABSTRACT FROM AUTHOR]