Mapping the present-day chemical abundance structure of the Solar neighbourhood: O & Si

Context. Large scale chemical abundance gradients in the Galactic disks, small-scale abundance structures, and the mean chemical abundance values in the Solar vicinity, are important constraints to Galactic chemo-dynamical formation and evolution models. The formation and evolution of stars, and interstellar gas and dust depends on the distribution and evolution of matter in the Galaxy. Therefore, metallicity structures within the Milky Way can be mapped from the abundance analysis of its gas and stars. Data. A sample of 379 mostly spectral type B main sequence stars within 1.5 kpc radius from the Sun, was observed with the MIKE high-resolution spectrograph on the Magellan 6.5-m telescope on Las Campanas in Chile in 2007. Projected rotational velocities and photometric effective temperatures were determined for these stars by Bragança et al. (2012). B-stars are good indicators for present-day cosmic abundances due to their short lifetimes. They preserve the interstellar medium abundances, which they were born from, in the photosphere, and they do not migrate far from their birth environment. Aims. The purpose of this Master’s project was to start mapping the present-day silicon and oxygen abundance structure of the Solar neighbourhood, by determining the stellar atmospheric parameters, and Si and O abundances, for the low-rotating (< 22 km/s ) subsample. The thesis at hand is part of an international study aimed to determine the elemental abundances of B-type main sequence stars near the Solar vicinity and in the outer Galactic disk (Bragança et al. 2012, 2015; Garmany et al. 2015, Bragança et al. in prep.). Methods. Line-profile fitting of Si, O and Balmer lines, with full NLTE synthetic spectra, and an iterative analysis methodology, was used to constrain stellar atmospheric parameters and elemental abundances at high accuracy and precision. Results & Conclusions. With this Master’s thesis, an extensive mapping the Solar neighbourhood has begun: stellar parameters, and Si and O abundances were established for 17 stars. The mean elemental abundance of the Solar neighbourhood of a 1.25 kpc radius, was found to be 7.42±0.13 dex for silicon and 8.73±0.06 dex for oxygen. The results are consistent with the cosmic abundance standard from Nieva & Przybilla (2012) within error-bars, and provide reliable present-day anchor points for Galactic chemical evolution models. However, the stars in our sample have on average smaller abundance values and the Solar neighbourhood seems to be more heterogeneous, than determined by Nieva & Przybilla (2012) study. Small scale abundance structures were not discovered, due to yet small sample size. In the future, other low-rotating stars in the observed stellar sample will be analysed, up to a v sin i = 80 km/s limit. This would amount to about 100 stars. Combined with Gaia DR2 positions, and chemical abundances for the fast rotating B-type stars in the Solar vicinity (Cazorla et al. 2017), would provide an unprecedented view of the present-day Solar neighbourhood.Vår galax, Vintergatan, innehåller bortåt 200 miljarder stjärnor av varierande åldrar och storlekar. Under en mörk och klar natt kan man se ungefär 2000 med blotta ögat. Detta är en liten del av det stora hela, men tillräckligt för att stimulera människors nyfikenhet. Vad är de gjorda av, och varför är de där de är? Enkla frågor, som har väldigt komplexa svar. Genom att kartlägga strukturen och den kemiska sammansättningen hos den unga nuvarande stjärnpopulationen i solens närhet avser detta arbete att besvara den första frågan och ge ytterligare ledtrådar till den andra. Vintergatans ursprung och utveckling finns bevarat i form av den kemiska sammansättningen och kinematiska egenskaperna hos dess stjärnor och gas, så genom att bestämma stjärnors kemiska sammansättning kan man få information om den miljö som de bildades från. Detta arbete har använt sig av massiva (2–16 Solmassa) huvudseriestjärnor för att bestämma den nutida ymnigheten av syre och kisel i solens närhet. Massiva stjärnor är utmärkta indikatorer för Vintergatans nutida kemiska sammansättning, av flera anledningar. För det första så har massiva stjärnor korta livstider, några miljoner till några tiotals miljoner år, att jämföras med Vintergatans ålder som är runt 13 miljarder år. För det andra så befinner de sig fortfarande på den plats de bildades, detta på grund av att de inte hunnit migrera nämnvärt på de få miljoner år de levt. För det tredje så är de väldigt luminösa, och således lätta att observera, vilket beror på att de har så höga temperaturer (10000–30000 K). Ymnigheten av olika grundämnen i atmosfärerna hos dessa stjärnor representerar den kemiska sammansättning som det interstellära mediet hade när de bildades. Den nutida sammansättningen av olika grundämnen i solens närhet utgör viktiga randvillkor för galaktiska kemisk-dynamiska utvecklingsmodeller eftersom de man vill att de skall resultera i realistiska Vintergatsmodeller. Riktmärket för Vintergatan är solens närhet som är det område som kan studeras med största noggrannhet och precision, eftersom stjärnorna är näraliggande och enkla att observera. Mer än 370 näraliggande (inom en radie av 1.5 kpc) massiva stjärnor observerades för detta projekt år 2007. Grova uppskattningar för stjärnornas rotationshastigheter och effektiva temperaturer gjordes av Bragança et al. (2012). Denna Masteruppsats har som mål att bestämma stjärnparametrar (effektiv temperature, ytgravitation, projicerad rotationsgahstighet, mikro- och makroturbulenshastigheter) och grundämneshalter på ett konsekvent sätt för de stjärnor som har låga rotationshastigheter. De observerade spektrumen jämfördes med syntetiskt spektrum, som genererats med hjälp av modellatmosfärer och atommodeller, för att analysera formerna på spektrallinjer. En linje-för-linje-baserad anpassningsmetod för kisel, syre, och vätelinjer användes, och statistiska metoder för att bestämma stjärnparametrar och grundämneshalter. Denna metod är väldigt tidskrävande - att analysera en stjärna tar några dagar upp till en vecka - men berikande. I detta Masterprojekt har 17 stjärnor i solens närhet analyserats för att kartlägga kisel- och syrehalter i solens närhet. Vi fann att solens närhet verkar vara aningen mindre homogen än vad som tidigare rapporterats. Dock så överensstämmer medelhalterna för solens närhet med tidigare liknande studier, samt med dessa grundämnens halter i solen. På grund av den kemiska utvecklingen i Vintergatan så borde yngre stjärnor generellt sett ha högre grundämneshalter än solen som är äldre. Dessa resultat antyder att solen bildades i de inre delarna av Vintergatan, som är mer berikade, och sedan migrerade till dess nuvarande position 8 kpc från Vintergatans centrum. Några småskaliga ymnighetsvariantioner kunde inte detekteras, antagligen beroende på det ännu begränsade antal stjärnor som analyserats.Framtida planer innefattar att analysera alla stjärnor i samplet, upp mot 100 stjärnor. Med denna Mastersuppsats har det detaljerade kartläggandet av solens närhet börjat

Physical Properties of the Nova Remnant Nova Persei 1901

http://www.ester.ee/record=b448451

The X-shooter Spectral Library and stellar population models

Astronomical objects are generally studied through observation-to-model comparisons. Galaxies are complex islands of stars, gas, dust and dark matter held together by gravity. They come in different shapes and sizes and can contain billions of stars. Galaxies have complicated histories shaped by galaxy interactions and mergers, and the evolution of their stars. The story of the formation and evolution of galaxies is written into the properties of their stars. To disentangle the history of a galaxy from observations, we need to create a set of models to describe the total starlight of a population of stars. This thesis looked at stellar population modelling from the stellar spectral library perspective. We aimed to develop the empirical X-shooter Spectral Library (XSL) and create stellar population models based on it. XSL is the most intricate library of spectra of observed stars to date. The full wavelength range of XSL spectra is 350-2480 nm, which covers simultaneously the optical-NIR regions. This is not common amongst empirical stellar spectral libraries, which typically cover a narrower (optical or NIR) range. XSL has a large number of spectra, totalling 830. It is the first empirical stellar library to emphasise stars in their advanced evolutionary stages, while also having good coverage of main sequence stars. With the JWST launched, ESO’s ELT and ESA’s Euclid mission on the horizon, XSL and the associated stellar population models will be useful tools in determining the hidden nature of distant galaxies. All of these telescopes will concentrate on the NIR wavelengths

The X-shooter Spectral Library (XSL): Data Release 3

We present the third data release (DR3) of the X-shooter Spectral Library (XSL). This moderate-to-high resolution, near-ultraviolet-to-near-infrared ($350-2480$ nm, R $\sim$ 10 000) spectral library is composed of 830 stellar spectra of 683 stars. DR3 improves upon the previous data release by providing the combined de-reddened spectra of the three X-shooter segments over the full $350-2480$ nm wavelength range. It also includes additional 20 M-dwarf spectra from the ESO archive. We provide detailed comparisons between this library and Gaia EDR3, MILES, NGSL, CaT library, and (E-)IRTF. The normalised rms deviation is better than $D=0.05$ or 5$\%$ for the majority of spectra in common between MILES (144 spectra of 180), NGSL (112$/$116), and (E-)IRTF (55$/$77) libraries. Comparing synthetic colours of those spectra reveals only negligible offsets and small rms scatter, such as the median offset(rms) 0.001$\pm$0.040 mag in the (box1-box2) colour of the UVB arm,-0.004$\pm$0.028 mag in (box3-box4) of the VIS arm, and -0.001$\pm$0.045 mag in (box2-box3) colour between the UVB and VIS arms, when comparing stars in common with MILES. We also find an excellent agreement between the Gaia published (BP-RP) colours and those measured from the XSL DR3 spectra, with a zero median offset and an rms scatter of 0.037 mag for 449 non-variable stars. The unmatched characteristics of this library, which combine a relatively high resolution, a large number of stars, and an extended wavelength coverage, will help us to bridge the gap between the optical and the near-IR studies of intermediate and old stellar populations, and to probe low-mass stellar systems.Comment: 26 pages, 25 figures, accepted to Astronomy & Astrophysics. The data are available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/ or on the XSL web-page http://xsl.astro.unistra.f

Modelling simple stellar populations in the near-ultraviolet to near-infrared with the X-shooter Spectral Library (XSL)

We present simple stellar population models based on the empirical X-shooter Spectral Library (XSL) from NUV to NIR wavelengths. The unmatched characteristics of relatively high resolution and extended wavelength coverage ($350-2480$ nm, $R\sim10\,000$) of the XSL population models bring us closer to bridging optical and NIR studies of intermediate and old stellar populations. It is now common to find good agreement between observed and predicted NUV and optical properties of stellar clusters due to our good understanding of the main-sequence and early giant phases of stars. However, NIR spectra of intermediate-age and old stellar populations are sensitive to cool K and M giants. The asymptotic giant branch, especially the thermally pulsing asymptotic giant branch, shapes the NIR spectra of $0.5-2$ Gyr old stellar populations; the tip of the red giant branch defines the NIR spectra of populations with ages larger than that. We construct sequences of the average spectra of static giants, variable-rich giants, and C-rich giants to include in the models separately. The models span the metallicity range $-2.2<[Fe/H]<+0.2$ and ages above 50 Myr, a broader range in the NIR than in other models based on empirical spectral libraries. Our models can reproduce the integrated optical colours of the Coma cluster galaxies at the same level as other semi-empirical models found in the literature. In the NIR, there are notable differences between the colours of the models and Coma cluster galaxies. The XSL models expand the range of predicted values of NIR indices compared to other models based on empirical libraries. Our models make it possible to perform in-depth studies of colours and spectral features consistently throughout the optical and the NIR range to clarify the role of evolved cool stars in stellar populations.Comment: 30 pages, 26 figures, accepted to Astronomy & Astrophysics, models will be available on http://xsl.astro.unistra.fr/ upon publishin

The wide-field, multiplexed, spectroscopic facility WEAVE : survey design, overview, and simulated implementation

Funding for the WEAVE facility has been provided by UKRI STFC, the University of Oxford, NOVA, NWO, Instituto de Astrofísica de Canarias (IAC), the Isaac Newton Group partners (STFC, NWO, and Spain, led by the IAC), INAF, CNRS-INSU, the Observatoire de Paris, Région Île-de-France, CONCYT through INAOE, Konkoly Observatory (CSFK), Max-Planck-Institut für Astronomie (MPIA Heidelberg), Lund University, the Leibniz Institute for Astrophysics Potsdam (AIP), the Swedish Research Council, the European Commission, and the University of Pennsylvania.WEAVE, the new wide-field, massively multiplexed spectroscopic survey facility for the William Herschel Telescope, will see first light in late 2022. WEAVE comprises a new 2-degree field-of-view prime-focus corrector system, a nearly 1000-multiplex fibre positioner, 20 individually deployable 'mini' integral field units (IFUs), and a single large IFU. These fibre systems feed a dual-beam spectrograph covering the wavelength range 366-959 nm at R ∼ 5000, or two shorter ranges at R ∼ 20,000. After summarising the design and implementation of WEAVE and its data systems, we present the organisation, science drivers and design of a five- to seven-year programme of eight individual surveys to: (i) study our Galaxy's origins by completing Gaia's phase-space information, providing metallicities to its limiting magnitude for ∼ 3 million stars and detailed abundances for ∼ 1.5 million brighter field and open-cluster stars; (ii) survey ∼ 0.4 million Galactic-plane OBA stars, young stellar objects and nearby gas to understand the evolution of young stars and their environments; (iii) perform an extensive spectral survey of white dwarfs; (iv) survey  ∼ 400 neutral-hydrogen-selected galaxies with the IFUs; (v) study properties and kinematics of stellar populations and ionised gas in z 1 million spectra of LOFAR-selected radio sources; (viii) trace structures using intergalactic/circumgalactic gas at z > 2. Finally, we describe the WEAVE Operational Rehearsals using the WEAVE Simulator.PostprintPeer reviewe

The wide-field, multiplexed, spectroscopic facility WEAVE: Survey design, overview, and simulated implementation

WEAVE, the new wide-field, massively multiplexed spectroscopic survey facility for the William Herschel Telescope, will see first light in late 2022. WEAVE comprises a new 2-degree field-of-view prime-focus corrector system, a nearly 1000-multiplex fibre positioner, 20 individually deployable 'mini' integral field units (IFUs), and a single large IFU. These fibre systems feed a dual-beam spectrograph covering the wavelength range 366$-$959\,nm at $R\sim5000$, or two shorter ranges at $R\sim20\,000$. After summarising the design and implementation of WEAVE and its data systems, we present the organisation, science drivers and design of a five- to seven-year programme of eight individual surveys to: (i) study our Galaxy's origins by completing Gaia's phase-space information, providing metallicities to its limiting magnitude for $\sim$3 million stars and detailed abundances for $\sim1.5$ million brighter field and open-cluster stars; (ii) survey $\sim0.4$ million Galactic-plane OBA stars, young stellar objects and nearby gas to understand the evolution of young stars and their environments; (iii) perform an extensive spectral survey of white dwarfs; (iv) survey $\sim400$ neutral-hydrogen-selected galaxies with the IFUs; (v) study properties and kinematics of stellar populations and ionised gas in $z<0.5$ cluster galaxies; (vi) survey stellar populations and kinematics in $\sim25\,000$ field galaxies at $0.3\lesssim z \lesssim 0.7$; (vii) study the cosmic evolution of accretion and star formation using $>1$ million spectra of LOFAR-selected radio sources; (viii) trace structures using intergalactic/circumgalactic gas at $z>2$. Finally, we describe the WEAVE Operational Rehearsals using the WEAVE Simulator.Comment: 41 pages, 27 figures, accepted for publication by MNRA

The wide-field, multiplexed, spectroscopic facility WEAVE: Survey design, overview, and simulated implementation

WEAVE, the new wide-field, massively multiplexed spectroscopic survey facility for the William Herschel Telescope, will see first light in late 2022. WEAVE comprises a new 2-degree field-of-view prime-focus corrector system, a nearly 1000-multiplex fibre positioner, 20 individually deployable 'mini' integral field units (IFUs), and a single large IFU. These fibre systems feed a dual-beam spectrograph covering the wavelength range 366−959\,nm at R∼5000, or two shorter ranges at R∼20000. After summarising the design and implementation of WEAVE and its data systems, we present the organisation, science drivers and design of a five- to seven-year programme of eight individual surveys to: (i) study our Galaxy's origins by completing Gaia's phase-space information, providing metallicities to its limiting magnitude for ∼3 million stars and detailed abundances for ∼1.5 million brighter field and open-cluster stars; (ii) survey ∼0.4 million Galactic-plane OBA stars, young stellar objects and nearby gas to understand the evolution of young stars and their environments; (iii) perform an extensive spectral survey of white dwarfs; (iv) survey ∼400 neutral-hydrogen-selected galaxies with the IFUs; (v) study properties and kinematics of stellar populations and ionised gas in z1 million spectra of LOFAR-selected radio sources; (viii) trace structures using intergalactic/circumgalactic gas at z>2. Finally, we describe the WEAVE Operational Rehearsals using the WEAVE Simulator