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- ItemMono-enriched stars and Galactic chemical evolution : Possible biases in observations and theory(Les Ulis : EDP Sciences, 2020) Hansen, C.J.; Koch, A.; Mashonkina, L.; Magg, M.; Bergemann, M.; Sitnova, T.; Gallagher, A.J.; Ilyin, I.; Caffau, E.; Zhang, H.W.; Strassmeier, K.G.; Klessen, R.S.A long sought after goal using chemical abundance patterns derived from metal-poor stars is to understand the chemical evolution of the Galaxy and to pin down the nature of the first stars (Pop III). Metal-poor, old, unevolved stars are excellent tracers as they preserve the abundance pattern of the gas from which they were born, and hence they are frequently targeted in chemical tagging studies. Here, we use a sample of 14 metal-poor stars observed with the high-resolution spectrograph called the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT) to derive abundances of 32 elements (34 including upper limits). We present well-sampled abundance patterns for all stars obtained using local thermodynamic equilibrium (LTE) radiative transfer codes and one-dimensional (1D) hydrostatic model atmospheres. However, it is currently well-known that the assumptions of 1D and LTE may hide several issues, thereby introducing biases in our interpretation as to the nature of the first stars and the chemical evolution of the Galaxy. Hence, we use non-LTE (NLTE) and correct the abundances using three-dimensional model atmospheres to present a physically more reliable pattern. In order to infer the nature of the first stars, we compare unevolved, cool stars, which have been enriched by a single event (“mono-enriched”), with a set of yield predictions to pin down the mass and energy of the Pop III progenitor. To date, only few bona fide second generation stars that are mono-enriched are known. A simple χ2-fit may bias our inferred mass and energy just as much as the simple 1D LTE abundance pattern, and we therefore carried out our study with an improved fitting technique considering dilution and mixing. Our sample presents Carbon Enhanced Metal-Poor (CEMP) stars, some of which are promising bona fide second generation (mono-enriched) stars. The unevolved, dwarf BD+09_2190 shows a mono-enriched signature which, combined with kinematical data, indicates that it moves in the outer halo and likely has been accreted onto the Milky Way early on. The Pop III progenitor was likely of 25.5 M⊙ and 0.6 foe (0.6 1051 erg) in LTE and 19.2 M⊙ and 1.5 foe in NLTE, respectively. Finally, we explore the predominant donor and formation site of the rapid and slow neutron-capture elements. In BD-10_3742, we find an almost clean r-process trace, as is represented in the star HD20, which is a “metal-poor Sun benchmark” for the r-process, while TYC5481-00786-1 is a promising CEMP-r/-s candidate that may be enriched by an asymptotic giant branch star of an intermediate mass and metallicity.
- ItemThe metal-poor end of the Spite plateau: II. Chemical and dynamical investigation(Les Ulis : EDP Sciences, 2021) Matas Pinto, A. M.; Spite, M.; Caffau, E.; Bonifacio, P.; Sbordone, L.; Sivarani, T.; Steffen, M.; Spite, F.; François, P.; Di Matteo, P.Context. The study of old, metal-poor stars deepens our knowledge on the early stages of the universe. In particular, the study of these stars gives us a valuable insight into the masses of the first massive stars and their emission of ionising photons. Aims. We present a detailed chemical analysis and determination of the kinematic and orbital properties of a sample of 11 dwarf stars. These are metal-poor stars, and a few of them present a low lithium content. We inspected whether the other elements also present anomalies. Methods. We analysed the high-resolution UVES spectra of a few metal-poor stars using the Turbospectrum code to synthesise spectral lines profiles. This allowed us to derive a detailed chemical analysis of Fe, C, Li, Na, Mg, Al, Si, CaI, CaII, ScII, TiII, Cr, Mn, Co, Ni, Sr, and Ba. Results. We find excellent coherence with the reference metal-poor First Stars sample. The lithium-poor stars do not present any anomaly of the abundance of the elements other than lithium. Among the Li-poor stars, we show that CS 22882-027 is very probably a blue-straggler. The star CS 30302-145, which has a Li abundance compatible with the plateau, has a very low Si abundance and a high Mn abundance. In many aspects, it is similar to the α-poor star HE 1424-0241, but it is less extreme. It could have been formed in a satellite galaxy and later been accreted by our Galaxy. This hypothesis is also supported by its kinematics.
- ItemThe Gaia-ESO Survey: Probing the lithium abundances in old metal-rich dwarf stars in the solar vicinity(Les Ulis : EDP Sciences, 2022) Dantas, M.L.L.; Guiglion, G.; Smiljanic, R.; Romano, D.; Magrini, L.; Bensby, T.; Chiappini, C.; Franciosini, E.; Nepal, S.; Tautvaišienė, G.; Gilmore, G.; Randich, S.; Lanzafame, A.C.; Heiter, U.; Morbidelli, L.; Prisinzano, L.; Zaggia, S.Context. Lithium (Li) is a fragile element that is produced in a variety of sites but can also be very easily depleted in stellar photospheres. Radial migration has been reported to explain the decrease in the upper envelope of Li measurements observed for relatively old metal-rich dwarf stars in some surveys. Aims. We test a scenario in which radial migration could affect the Li abundance pattern of dwarf stars in the solar neighbourhood. This may confirm that the Li abundances in these stars cannot serve as a probe for the Li abundance in the interstellar medium (ISM). In other words, to probe the evolution of the Li abundance in the local ISM, it is crucial that stellar intruders be identified and removed from the adopted sample. Methods. We used the high-quality data (including Li abundances) from the sixth internal Data Release of the Gaia-ESO survey. In this sample we grouped stars by similarity in chemical abundances via hierarchical clustering. Our analysis treats both measured Li abundances and upper limits. Results. The Li envelope of the previously identified radially migrated stars is well below the benchmark meteoritic value (<3.26 dex); the star with the highest detected abundance has A(Li) = 2.76 dex. This confirms the previous trends observed for old dwarf stars (median ages ~ 8 Gyr), where Li decreases for [Fe/H] ≳ 0. Conclusions. This result is supporting evidence that the abundance of Li measured in the upper envelope of old dwarf stars should not be considered a proxy for the ISM Li. Our scenario also indicates that the stellar yields for [M/H] >0 should not be decreased, as recently proposed in the literature. Our study backs recent studies that claim that old dwarfs on the hot side of the dip are efficient probes of the ISM abundance of Li, provided atomic diffusion does not significantly lower the initial Li abundance in the atmospheres of metal-rich objects.
- ItemThe eROSITA X-ray telescope on SRG(Les Ulis : EDP Sciences, 2021) Predehl, P.; Andritschke, R.; Arefiev, V.; Babyshkin, V.; Batanov, O.; Becker, W.; Böhringer, H.; Bogomolov, A.; Boller, T.; Borm, K.; Bornemann, W.; Bräuninger, H.; Brüggen, M.; Brunner, H.; Brusa, M.; Bulbul, E.; Buntov, M.; Burwitz, V.; Burkert, W.; Clerc, N.; Churazov, E.; Coutinho, D.; Dauser, T.; Dennerl, K.; Doroshenko, V.; Eder, J.; Emberger, V.; Eraerds, T.; Finoguenov, A.; Freyberg, M.; Friedrich, P.; Friedrich, S.; Fürmetz, M.; Georgakakis, A.; Gilfanov, M.; Granato, S.; Grossberger, C.; Gueguen, A.; Gureev, P.; Haberl, F.; Hälker, O.; Hartner, G.; Hasinger, G.; Huber, H.; Ji, L.; Kienlin, A. v.; Kink, W.; Korotkov, F.; Kreykenbohm, I.; Lamer, G.; Lomakin, I.; Lapshov, I.; Liu, T.; Maitra, C.; Meidinger, N.; Menz, B.; Merloni, A.; Mernik, T.; Mican, B.; Mohr, J.; Müller, S.; Nandra, K.; Nazarov, V.; Pacaud, F.; Pavlinsky, M.; Perinati, E.; Pfeffermann, E.; Pietschner, D.; Ramos-Ceja, M. E.; Rau, A.; Reiffers, J.; Reiprich, T. H.; Robrade, J.; Salvato, M.; Sanders, J.; Santangelo, A.; Sasaki, M.; Scheuerle, H.; Schmid, C.; Schmitt, J.; Schwope, A.; Shirshakov, A.; Steinmetz, M.; Stewart, I.; Strüder, L.; Sunyaev, R.; Tenzer, C.; Tiedemann, L.; Trümper, J.; Voron, V.; Weber, P.; Wilms, J.; Yaroshenko, V.eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the primary instrument on the Spectrum-Roentgen-Gamma (SRG) mission, which was successfully launched on July 13, 2019, from the Baikonour cosmodrome. After the commissioning of the instrument and a subsequent calibration and performance verification phase, eROSITA started a survey of the entire sky on December 13, 2019. By the end of 2023, eight complete scans of the celestial sphere will have been performed, each lasting six months. At the end of this program, the eROSITA all-sky survey in the soft X-ray band (0.2-2.3 keV) will be about 25 times more sensitive than the ROSAT All-Sky Survey, while in the hard band (2.3-8 keV) it will provide the first ever true imaging survey of the sky. The eROSITA design driving science is the detection of large samples of galaxy clusters up to redshifts z > 1 in order to study the large-scale structure of the universe and test cosmological models including Dark Energy. In addition, eROSITA is expected to yield a sample of a few million AGNs, including obscured objects, revolutionizing our view of the evolution of supermassive black holes. The survey will also provide new insights into a wide range of astrophysical phenomena, including X-ray binaries, active stars, and diffuse emission within the Galaxy. Results from early observations, some of which are presented here, confirm that the performance of the instrument is able to fulfil its scientific promise. With this paper, we aim to give a concise description of the instrument, its performance as measured on ground, its operation in space, and also the first results from in-orbit measurements.
- ItemMUSE crowded field 3D spectroscopy in NGC 300: III. Characterizing extremely faint HII regions and diffuse ionized gas(Les Ulis : EDP Sciences, 2022) Micheva, Genoveva; Roth, Martin M.; Weilbacher, Peter M.; Morisset, Christophe; Castro, Norberto; Monreal Ibero, Ana; Soemitro, Azlizan A.; Maseda, Michael V.; Steinmetz, Matthias; Brinchmann, JarleContext. There are known differences between the physical properties of H II and diffuse ionized gas (DIG). However, most of the studied regions in the literature are relatively bright, with log10 L(Hα)[erg s-1] ≳37. Aims. We compiled an extremely faint sample of 390 H II regions with a median Hα luminosity of 34.7 in the flocculent spiral galaxy NGC 300, derived their physical properties in terms of metallicity, density, extinction, and kinematics, and performed a comparative analysis of the properties of the DIG. Methods. We used MUSE data of nine fields in NGC 300, covering a galactocentric distance of zero to ~450 arcsec (~4 projected kpc), including spiral arm and inter-arm regions. We binned the data in dendrogram leaves and extracted all strong nebular emission lines. We identified H II and DIG regions and compared their electron densities, metallicity, extinction, and kinematic properties. We also tested the effectiveness of unsupervised machine-learning algorithms in distinguishing between the H II and DIG regions. Results. The gas density in the H II and DIG regions is close to the low-density limit in all fields. The average velocity dispersion in the DIG is higher than in the H II regions, which can be explained by the DIG being 1.8 kK hotter than H II gas. The DIG manifests a lower ionization parameter than H II gas, and the DIG fractions vary between 15-77%, with strong evidence of a contribution by hot low-mass evolved stars and shocks to the DIG ionization. Most of the DIG is consistent with no extinction and an oxygen metallicity that is indistinguishable from that of the H II gas. We observe a flat metallicity profile in the central region of NGC 300, without a sign of a gradient. Conclusions. The differences between extremely faint H II and DIG regions follow the same trends and correlations as their much brighter cousins. Both types of objects are so heterogeneous, however, that the differences within each class are larger than the differences between the two classes.
- ItemSurface brightness-colour relations of dwarf stars from detached eclipsing binaries: I. Calibrating sample(Les Ulis : EDP Sciences, 2022) Graczyk, D.; Pietrzyński, G.; Galan, C.; Southworth, J.; Gieren, W.; Kałuszyński, M.; Zgirski, B.; Gallenne, A.; Górski, M.; Hajdu, G.; Karczmarek, P.; Kervella, P.; Maxted, P. F. L.; Nardetto, N.; Narloch, W.; Pilecki, B.; Pych, W.; Rojas Garcia, G.; Storm, J.; Suchomska, K.; Taormina, M.; Wielgórski, P.Aims. Surface brightness - colour relations (SBCRs) are very useful tools for predicting the angular diameters of stars. They offer the possibility to calculate very precise spectrophotometric distances by the eclipsing binary method or the Baade-Wesselink method. Double-lined Detached Eclipsing Binary stars (SB2 DEBs) with precisely known trigonometric parallaxes allow for a calibration of SBCRs with unprecedented precision. In order to improve such calibrations, it is important to enlarge the calibration sample of suitable eclipsing binaries with very precisely determined physical parameters. Methods. We carefully chose a sample of ten SB2 DEBs in the solar neighbourhood which contain inactive main-sequence components. The components have spectral types from early A to early K. All systems have high-precision parallaxes from the Gaia mission. We analysed high precision ground- and space-based photometry simultaneously with the radial velocity curves derived from HARPS spectra. We used spectral disentangling to obtain the individual spectra of the components and used these to derive precise atmospheric parameters and chemical abundances. For almost all components, we derived precise surface temperatures and metallicities. Results. We derived absolute dimensions for 20 stars with an average precision of 0.2% and 0.5% for masses and radii, respectively. Three systems show slow apsidal motion. One system, HD 32129, is most likely a triple system with a much fainter K6V companion. Also three systems contain metallic-line components and show strong enhancements of barium and ittrium. Conclusions. The components of all systems compare well to the SBCR derived before from the detached eclipsing binary stars. With a possible exception of HD 32129, they can be used to calibrate SBCRs with a precision better than 1% with available Gaia DR3 parallaxes.
- ItemAbsolute dimensions and apsidal motion of the eclipsing binaries V889 Aquilae and V402 Lacertae(Les Ulis : EDP Sciences, 2022) Baroch, D.; Giménez, A.; Morales, J. C.; Ribas, I.; Herrero, E.; Perdelwitz, V.; Jordi, C.; Granzer, T.; Allende Prieto, C.Context. Double-lined eclipsing binaries allow the direct determination of masses and radii, which are key for testing stellar models. With the launch of the TESS mission, many well-known eclipsing binaries have been observed at higher photometric precision, permitting the improvement of the absolute dimension determinations. Aims. Using TESS data and newly obtained spectroscopic observations, we aim to determine the masses and radii of the eccentric eclipsing binary systems V889 Aql and V402 Lac, together with their apsidal motion parameters. Methods. We simultaneously modelled radial velocity curves and times of eclipse for each target to precisely determine the orbital parameters of the systems, which we used to analyse the light curves and then obtain their absolute dimensions. We compared the obtained values with those predicted by theoretical models. Results. We determined masses and radii of the components of both systems with relative uncertainties lower than 2%. V889 Aql is composed of two stars with masses 2:17±0:02 M⊙ and 2:13±0:01 M⊙ and radii 1:87±0:04 R⊙ and 1:85±0:04 R⊙.We find conclusive evidence of the presence of a third body orbiting V889 Aql with a period of 67 yr. Based on the detected third light and the absence of signal in the spectra, we suggest that this third body could in turn be a binary composed of two ±1.4 M⊙ stars. V402 Lac is composed of two stars with masses 2:80 ± 0:05 M⊙ and 2:78 ± 0:05 M⊙ and radii 2:38 ± 0:03 R⊙ and 2:36 ± 0:03 R⊙. The times of minimum light are compatible with the presence of a third body for this system too, although its period is not yet fully sampled. In both cases we have found a good agreement between the observed apsidal motion rates and the model predictions.
- ItemGaia Early Data Release 3: Gaia photometric science alerts(Les Ulis : EDP Sciences, 2021) Hodgkin, S.T.; Harrison, D.L.; Breedt, E.; Wevers, T.; Rixon, G.; Delgado, A.; Yoldas, A.; Kostrzewa-Rutkowska, Z.; Wyrzykowski, Ł.; van Leeuwen, M.; Blagorodnova, N.; Serraller, I.; Steeghs, D.; Sullivan, M.; Szabados, L.; Szegedi-Elek, E.; Tisserand, P.; Tomasella, L.; van Velzen, S.; Whitelock, P.A; Wilson, R.W.; Campbell, H.; Young, D.R.; Eappachen, D.; Fraser, M.; Ihanec, N.; Koposov, S.E.; Kruszyńska, K.; Marton, G.; Rybicki, K.A.; Brown, A.G.A.; Burgess, P. W.; Busso, G.; Cowell, S.; De Angeli, F.; Diener, C.; Evans, D.W.; Gilmore, G.; Holland, G.; Jonker, P.G.; van Leeuwen, F.; Mignard, F.; Osborne, P.J.; Portell, J.; Prusti, T.; Richards, P.J.; Riello, M.; Seabroke, G.M.; Walton, N.A.; Ábrahám, Péter; Altavilla, G.; Baker, S.G.; Bastian, U.; O'Brien, P.; de Bruijne, J.; Butterley, T.; Carrasco, J.M.; Castañeda, J.; Clark, J.S.; Clementini, G.; Copperwheat, C.M.; Cropper, M.; Damljanovic, G.; Davidson, M.; Davis, C.J.; Dennefeld, M.; Dhillon, V.S.; Dolding, C.; Dominik, M.; Esquej, P.; Eyer, L.; Fabricius, C.; Fridman, M.; Froebrich, D.; Garralda, N.; Gomboc, A.; González-Vidal, J.J.; Guerra, R.; Hambly, N.C.; Hardy, L.K.; Holl, B.; Hourihane, A.; Japelj, J.; Kann, D.A.; Kiss, C.; Knigge, C.; Kolb, U.; Komossa, S.; Kóspál, Á.; Kovács, G.; Kun, M.; Leto, G.; Lewis, F.; Littlefair, S.P.; Mahabal, A.A.; Mundell, C.G.; Nagy, Z.; Padeletti, D.; Palaversa, L.; Pigulski, A.; Pretorius, M.L.; van Reeven, W.; Ribeiro, V.A.R.M.; Roelens, M.; Rowell, N.; Schartel, N.; Scholz, A.; Schwope, A.; Sipőcz, B.M.; Smartt, S.J.; Smith, M.D.Context. Since July 2014, the Gaia mission has been engaged in a high-spatial-resolution, time-resolved, precise, accurate astrometric, and photometric survey of the entire sky. Aims. We present the Gaia Science Alerts project, which has been in operation since 1 June 2016. We describe the system which has been developed to enable the discovery and publication of transient photometric events as seen by Gaia. Methods. We outline the data handling, timings, and performances, and we describe the transient detection algorithms and filtering procedures needed to manage the high false alarm rate. We identify two classes of events: (1) sources which are new to Gaia and (2) Gaia sources which have undergone a significant brightening or fading. Validation of the Gaia transit astrometry and photometry was performed, followed by testing of the source environment to minimise contamination from Solar System objects, bright stars, and fainter near-neighbours. Results. We show that the Gaia Science Alerts project suffers from very low contamination, that is there are very few false-positives. We find that the external completeness for supernovae, CE = 0.46, is dominated by the Gaia scanning law and the requirement of detections from both fields-of-view. Where we have two or more scans the internal completeness is CI = 0.79 at 3 arcsec or larger from the centres of galaxies, but it drops closer in, especially within 1 arcsec. Conclusions. The per-Transit photometry for Gaia transients is precise to 1% at G = 13, and 3% at G = 19. The per-Transit astrometry is accurate to 55 mas when compared to Gaia DR2. The Gaia Science Alerts project is one of the most homogeneous and productive transient surveys in operation, and it is the only survey which covers the whole sky at high spatial resolution (subarcsecond), including the Galactic plane and bulge. © S. T. Hodgkin et al. 2021.
- ItemX-ray emission from a rapidly accreting narrow-line Seyfert 1 galaxy at z = 6.56(Les Ulis : EDP Sciences, 2023) Wolf, J.; Nandra, K.; Salvato, M.; Buchner, J.; Onoue, M.; Liu, T.; Arcodia, R.; Merloni, A.; Ciroi, S.; Di Mille, F.; Burwitz, V.; Brusa, M.; Ishimoto, R.; Kashikawa, N.; Matsuoka, Y.; Urrutia, T.; Waddell, S.G.H.The space density of X-ray-luminous, blindly selected active galactic nuclei (AGN) traces the population of rapidly accreting super-massive black holes through cosmic time. It is encoded in the X-ray luminosity function, whose bright end remains poorly constrained in the first billion years after the Big Bang as X-ray surveys have thus far lacked the required cosmological volume. With the eROSITA Final Equatorial-Depth Survey (eFEDS), the largest contiguous and homogeneous X-ray survey to date, X-ray AGN population studies can now be extended to new regions of the luminosity-redshift space (L2-10 keV > 1045 erg s-1 and z > 6). Aims. The current study aims at identifying luminous quasars at z > 5:7 among X-ray-selected sources in the eFEDS field in order to place a lower limit on black hole accretion well into the epoch of re-ionisation. A secondary goal is the characterisation of the physical properties of these extreme coronal emitters at high redshifts. Methods. Cross-matching eFEDS catalogue sources to optical counterparts from the DESI Legacy Imaging Surveys, we confirm the low significance detection with eROSITA of a previously known, optically faint z = 6:56 quasar from the Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs) survey. We obtained a pointed follow-up observation of the source with the Chandra X-ray telescope in order to confirm the low-significance eROSITA detection. Using new near-infrared spectroscopy, we derived the physical properties of the super-massive black hole. Finally, we used this detection to infer a lower limit on the black hole accretion density rate at z > 6. Results. The Chandra observation confirms the eFEDS source as the most distant blind X-ray detection to date. The derived X-ray luminosity is high with respect to the rest-frame optical emission of the quasar.With a narrow Mgii line, low derived black hole mass, and high Eddington ratio, as well as its steep photon index, the source shows properties that are similar to local narrow-line Seyfert 1 galaxies, which are thought to be powered by young super-massive black holes. In combination with a previous high-redshift quasar detection in the field, we show that quasars with L2-10 keV > 1045 erg s-1 dominate accretion onto super-massive black holes at z _ 6.
- ItemNewly formed downflow lanes in exploding granules in the solar photosphere(Les Ulis : EDP Sciences, 2021) Ellwarth, M.; Fischer, C.E.; Vitas, N.; Schmiz, S.; Schmidt, W.Context. Exploding granules have drawn renewed interest because of their interaction with the magnetic field (either emerging or already present). Especially the newly forming downflow lanes developing in their centre seem to be eligible candidates for the intensification of magnetic fields. We analyse spectroscopic data from two different instruments in order to study the intricate velocity pattern within the newly forming downflow lanes in detail. Aims. We aim to examine general properties of a number of exploding granules, such as their lifetime and extend. To gain a better understanding of the formation process of the developing intergranular lane in exploding granules, we study the temporal evolution and height dependence of the line-of-sight velocities at their formation location. Additionally, we search for evidence that exploding granules act as acoustic sources. Methods. We investigated the evolution of several exploding granules using data taken with the Interferometric Bidimensional Spectrometer and the Imaging Magnetograph eXperiment. Velocities for different heights of the solar atmosphere were determined by computing bisectors of the Fe I 6173.0 Å and the Fe I 5250.2 Å lines. We performed a wavelet analysis to study the intensity and velocity oscillations within and around exploding granules. We also compared our observational findings with predictions of numerical simulations. Results. Exploding granules have significantly longer lifetimes (10 to 15 min) than regular granules. Exploding granules larger than 3.8″ form an independent intergranular lane during their decay phase, while smaller granules usually fade away or disappear into the intergranular area (we find only one exception of a smaller exploding granule that also forms an intergranular lane). For all exploding granules that form a new intergranular downflow lane, we find a temporal height-dependent shift with respect to the maximum of the downflow velocity. Our suggestion that this results from a complex atmospheric structure within the newly forming downflow lane is supported by the comparison with synthesised profiles inferred from the simulations. We found an enhanced wavelet power with periods between 120 s to 190 s seen in the intensity and velocity oscillations of high photospheric or chromospheric spectral lines in the region of the dark core of an exploding granule. © M. Ellwarth et al. 2021.