We report the search of RR Lyrae in the vicinity of a newly discovered ultrafaint dwarf galaxy, Aquarius III. Based on the known RR Lyrae catalogs and $gri$-band light curves retrieved from public archives, we identified a RR Lyrae with distance, metallicity, and proper motion consistent with Aquarius III. Therefore, this RR Lyrae is the first variable star identified to be associated with Aquarius III, despite its projected distance is more than 15 times the half-light radius of Aquarius III. On the other hand, a dedicated time-series monitoring of the central part of Aquarius III, out to a projected radius of approximately four half-light radius, revealed there is no RR Lyrae in this region. We ran a set of synthetic color-magnitude diagrams with properties similar to Aquarius III, and found a non-negligible probability that Aquarius III could have (at least one) RR Lyrae. We have also identified a RR Lyrae candidate but most likely it is a background halo star.
In this paper we present the analysis of Hubble Space Telescope (HST) observations of the globular cluster Omega Centauri. Our analysis combines data obtained in this work with previously published HST data from an earlier article of this series and encompasses a broad portion of the cluster's radial extension. Our findings reveal a significant radial variation in the fraction of stars within the two most populous stellar populations showing that one of the main second-population groups (referred to as bMS) is more centrally concentrated than the first-population group (referred to as rMS). Additionally, we explore the spatial variations of the other less populous stellar populations (referred to as MSa and MSd) and find a qualitatively similar, but weaker, radial decrease in the fraction of stars in these populations at larger distances from the cluster centre. Only one of the populations identified (MSe) does not show any significant radial variation.
A primeira galáxia anã de brilho ultrabaixo UFD (ultra-faint dwarf) foi descoberta no levantamento SDSS (Sloan Digital Sky Survey) em 2005, iniciando uma busca que resultou na descoberta de dezenas de galáxias anãs similares. Trata-se de uma continuação das galáxias anãs clássicas conhecidas antes do levantamento SDSS em direção a luminosidades e metalicidades mais baixas. O estudo da cinemática estelar mostra que as galáxias UFD possuem mais matéria escura que as galáxias anãs clássicas. As observações espectroscópicas revelam que as estrelas nas galáxias UFD são entre as mais velhas conhecidas e as de mais baixa metalicidade. As abundâncias de ferro Fe e de outros elementos químicos mostram grandes variações em consequência de formação estelar extensa no passado. A análise de estrelas individuais nas galáxias UFD em um intervalo estreito de massa estelar é consistente com a hipótese de que se formaram muitas estrelas de alta massa nas galáxias UFD e que o processo de formação estelar terminou na época de reionização do universo no redshift z ∼ 6. Uma vez que as galáxias anãs de brilho ultrabaixo UFD são os sistemas estelares mais velhos e os mais escuros conhecidos no universo, as mesmas são excelentes laboratórios para estudar a formação das primeiras galáxias no universo bem como o comportamento de matéria escura em pequena escala.
Formed at an early stage of gas-phase ion-molecule chemistry, hydrides -- molecules containing a heavy element covalently bonded to one or more hydrogen atoms -- play an important role in interstellar chemistry as they are the progenitors of larger and more complex species in the interstellar medium. In recent years, the careful analysis of the spectral signatures of hydrides have led to their use as tracers of different constituents, and phases of the interstellar medium and in particular the more diffuse environments. Diffuse clouds form an essential link in the stellar gas life-cycle as they connect both the late and early stages of stellar evolution. As a result, diffuse clouds are continuously replenished by material which makes them reservoirs for heavy elements and hence ideal laboratories for the study of astrochemistry. This review will journey through a renaissance of hydride observations detailing puzzling hydride discoveries and chemical mysteries with special focus carbon-bearing hydrides to demonstrate the big impact of these small molecules and ending with remarks on the future of their studies.
Abstract For several years we have been running an “astro-animation” class (AstroAnimation.org) at the Maryland Institute College of Art (MICA) in Baltimore where students work in tandem with research scientists from NASA Goddard and elsewhere to create animations. These combine results of cutting-edge research with an artist’s eye to create novel presentations of scientific results. The animations have been used for scientific outreach and educational purposes, including presentations at museums, and art, STEAM, and science fiction festivals. Astronomy has broad public interest with a “wow” factor related to black holes, dark matter, life in the universe and more. Animation is an ideal medium since it combines creative approaches, is highly popular, and the films produced are readily available for distribution.
Aris Tritsis, Harold W. Yorke, Konstantinos Tassis
We describe PyRaTE, a new, non-local thermodynamic equilibrium (non-LTE) line radiative transfer code developed specifically for post-processing astrochemical simulations. Population densities are estimated using the escape probability method. When computing the escape probability, the optical depth is calculated towards all directions with density, molecular abundance, temperature and velocity variations all taken into account. A very easy-to-use interface, capable of importing data from simulations outputs performed with all major astrophysical codes, is also developed. The code is written in Python using an `embarrassingly parallel' strategy and can handle all geometries and projection angles. We benchmark the code by comparing our results with those from RADEX (van der Tak et al. 2007) and against analytical solutions and present case studies using hydrochemical simulations. The code is available on GitHub (https://github.com/ArisTr/PyRaTE).
Paul A Crowther, Norberto Castro, Chris Evans
et al.
We provide an overview of Science Verification MUSE observations of NGC 2070, the central region of the Tarantula Nebula in the Large Magellanic Cloud. Integral-field spectroscopy of the central 2' x 2' region provides the first complete spectroscopic census of its massive star content, nebular conditions and kinematics. The star-formation surface density of NGC 2070 is reminiscent of the intense star-forming knots of high-redshift galaxies, with nebular conditions similar to low-redshift Green Pea galaxies, some of which are Lyman continuum leakers. Uniquely, MUSE permits the star-formation history of NGC 2070 to be studied from both spatially-resolved and integrated-light spectroscopy.
We present results of hydrodynamic simulations of massive star forming regions with and without protostellar jets. We show that jets change the normalization of the stellar mass accretion rate, but do not strongly affect the dynamics of star formation. In particular, $M_*(t) \propto f^2 (t-t_*)^2$ where $f = 1 - f_{\rm jet}$ is the fraction of mass accreted onto the protostar, $f_{\rm jet}$ is the fraction ejected by the jet, and $(t-t_*)^2$ is the time elapsed since the formation of the first star. The star formation efficiency is nonlinear in time. We find that jets have only a small effect (of order 25\%) on the accretion rate onto the protostellar disk (the "raw" accretion rate). We show that the small scale structure -- the radial density, velocity, and mass accretion profiles are very similar in the jet and no-jet cases. Finally, we show that the inclusion of jets does drive turbulence but only on small (parsec) scales.
Colin A. Navin, Sarah L. Martell, Daniel B. Zucker
M3 and M13 are Galactic globular clusters with previous reports of surrounding stellar halos. We present the results of a search for members and extratidal cluster halo stars within and outside of the tidal radius of these clusters in the LAMOST Data Release 1. We find seven candidate cluster members (inside the tidal radius) of both M3 and M13 respectively. In M3 we also identify eight candidate extratidal cluster halo stars at distances up to ~9.8 times the tidal radius, and in M13 we identify 12 candidate extratidal cluster halo stars at distances up to ~13.8 times the tidal radius. These results support previous indications that both M3 and M13 are surrounded by extended stellar halos, and we find that the GC destruction rates corresponding to the observed mass loss are generally significantly higher than theoretical studies predict.
C. A. Martínez-Barbosa, A. G. A. Brown, S. Portegies Zwart
We perform realistic simulations of the Sun's birth cluster in order to predict the current distribution of solar siblings in the Galaxy. We study the possibility of finding the solar siblings in the Gaia catalogue by using only positional and kinematic information. We find that the number of solar siblings predicted to be observed by Gaia will be around 100 in the most optimistic case, and that a phase space only search in the Gaia catalogue will be extremely difficult. It is therefore mandatory to combine the chemical tagging technique with phase space selection criteria in order to have any hope of finding the solar siblings.
The Hopkins Ultraviolet Telescope (HUT) was a 0.9 m telescope and moderate-resolution (Δλ = 3 Å) far-ultraviolet (820–1850 Å) spectrograph that flew twice on the space shuttle, in 1990 December (Astro-1, STS-35) and 1995 March (Astro-2, STS-67). The resulting spectra were originally archived in a nonstandard format that lacked important descriptive metadata. To increase their utility, we have modified the original data-reduction software to produce a new and more user-friendly data product, a time-tagged photon list similar in format to the Intermediate Data Files (IDFs) produced by the Far Ultraviolet Spectroscopic Explorer calibration pipeline. We have transferred all relevant pointing and instrument-status information from locally-archived science and engineering databases into new FITS header keywords for each data set. Using this new pipeline, we have reprocessed the entire HUT archive from both missions, producing a new set of calibrated spectral products in a modern FITS format that is fully compliant with Virtual Observatory requirements. For each exposure, we have generated quick-look plots of the fully-calibrated spectrum and associated pointing history information. Finally, we have retrieved from our archives HUT TV guider images, which provide information on aperture positioning relative to guide stars, and converted them into FITS-format image files. All of these new data products are available in the new HUT section of the Mikulski Archive for Space Telescopes (MAST), along with historical and reference documents from both missions. In this article, we document the improved data-processing steps applied to the data and show examples of the new data products.
We present detailed chemical abundances for $>$20 elements in $\sim$30 globular clusters in M31. These results have been obtained using high resolution ($λ/Δλ\sim$24,000) spectra of their integrated light and analyzed using our original method. The globular clusters have galactocentric radii between 2.5 kpc and 117 kpc, and therefore provide abundance patterns for different phases of galaxy formation recorded in the inner and outer halo of M31. We find that the clusters in our survey have a range in metallicity of $-2.2<$[Fe/H]$<-0.11$. The inner halo clusters cover this full range, while the outer halo globular clusters at R$>$20 kpc have a small range in abundance of [Fe/H]$=-1.6 \pm 0.10$. We also measure abundances of alpha, r- and s-process elements. These results constitute the first abundance pattern constraints for old populations in M31 that are comparable to those known for the Milky Way halo.
NGC 2438 is a classical multiple shell or halo planetary nebula (PN). Its central star and the main nebula are well studied. Also it was target of various hydrodynamic simulations (Corradi et al. 2000). This initiated a discussion whether the haloes are mainly containing recombined gas (Schoenberner et al. 2002), or if they are still ionized (Armsdorfer et al. 2003). An analysis of narrow-band images and long slit spectra at multiple slit positions was done to obtain a deeper look on morphological details and the properties of the outer shell and halo. For this work there was data available from ESO (direct imaging and long slit spectroscopy) and from SAAO (spectroscopic observations using a small slit - scanning over the whole nebula). Using temperature measurements from emission lines resulted in an electron temperature which clearly indicates a fully ionized stage. Additionally measurements of the electron density suggest a variation of the filling factor.