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Stars in low-mass dwarf galaxies show a larger range in their chemical properties than those in the Milky Way halo. The slower star formation efficiency make dwarf galaxies ideal systems for testing nucleosynthetic yields. Not only are alpha-poor stars found at lower metallicities, and a higher fraction of carbon-enhanced stars, but we are also finding stars in dwarf galaxies that appear to be iron-rich. These are compared with yields from a variety of supernova predictions.
We briefly review what is currently known of 14N/15N ratios in interstellar molecules. We summarize the fractionation ratios measured in HCN, HNC, CN, N2 and NH3, and compare these to theoretical predictions and to the isotopic inventory of cometary volatiles.
The light curves of spotted, rotating stars are often non-sinusoidal and Quasi-Periodic (QP) and a strictly periodic sinusoid is therefore not a representative generative model. Ideally, a physical model of the stellar surface would be conditioned on the data, however the parameters of such models can be highly degenerate.
The Javalambre-Physics of the Accelerating Universe Astrophysical Survey (J-PAS) is a narrow-band imaging, very wide field cosmological survey. It will last 5 years and will observe 8500 sq. deg. of the sky. There will be 54 contiguous narrow-band filters of 145Å FWHM, from 3,500 to 10,000Å. Two broad-band filters will be added at the extremes, UV and IR, plus the 3–g, r, and i– SDSS filters. Thus, J-PAS can be an important tool to search for new planetary nebulae (PNe) at the halo, increasing their numbers, because only 14 of them have been convincingly identified in the literature. Halo PNe are able to reveal precious information for the study of stellar evolution and the early chemical conditions of the Galaxy. The characteristic low continuum and intense emission lines of PNe make them good objects to be searched by J-PAS. Though covering a significantly smaller sky area, data from the ALHAMBRA survey were used to test our J-PAS strategy to search for PNe. Our first results are shown in this contribution.
We explore the radial (p-mode) stability of stars across a wide range of mass (0.2 < M < 50 M⊙), composition (0 < X < 0.7, Z = 0.001, 0.02), effective temperature, and luminosity. We identify the instability boundaries associated with low- to high-order radial oscillations (0 ⩽ n ⩽ 13). The instability boundaries are a strong function of both composition and radial order (n). The classical blue edge shifts to higher effective temperature and luminosity with decreasing hydrogen abundance. High-order modes are more easily excited and small islands of high radial-order instability develop, some of which correspond with real stars. Driving in all cases is by the classical κ-mechanism and, at high luminosity-to-mass ratio, strange-mode instability. We identify regions of parameter space where new classes of pulsating variable have recently or may, in future, be discovered. The majority of these are associated with reduced hydrogen abundance in the envelope.
Astronomy for development projects conceive of development in very broad terms and seek to affect a wide range of social outcomes. The histories of education, development economics and science communication research indicate that positive social impacts are often difficult to achieve. Without a scientific approach, astronomy's potential as a tool for development may never be realised nor recognised. Evidence-informed project design increases the chances of a project's success and likely impact while reducing the risk of unintended negative outcomes. The IAU Office of Astronomy for Development (OAD) Impact Cycle is presented here as a possible framework for integrating evaluation and evidence-based practice in global Astronomy outreach and education delivery. The suggested framework offers a way to gradually accumulate knowledge about which approaches are effective and which are not, enabling the astronomy community to gradually increase its social impact by building on its successes.
In this study we tested the prospects of using 2D chemical abundance ratio distributions (CARDs) found in stars of the stellar halo to determine its formation history. First, we used simulated data from eleven “MW-like” halos to generate satellite template sets of 2D CARDs of accreted dwarf satellites which are comprised of accreted dwarfs from various mass regimes and epochs of accretion. Next, we randomly drew samples of ~ 103–4 mock observations of stellar chemical abundance ratios ([α/Fe], [Fe/H]) from those eleven halos to generate samples of the underlying densities for our CARDs to be compared to our templates in our analysis. Finally, we used the expectation-maximization algorithm to derive accretion histories in relation to the satellite template set (STS) used and the sample size. For certain STS used we typically can identify the relative mass contributions of all accreted satellites to within a factor of 2. We also find that this method is particularly sensitive to older accretion events involving low-luminous dwarfs e.g. ultra-faint dwarfs — precisely those events that are too ancient to be seen by phase-space studies of stars and too faint to be seen by high-z studies of the early Universe. Since our results only exploit two chemical dimensions and near-future surveys promise to provide ~ 6–9 dimensions, we conclude that these new high-resolution spectroscopic surveys of the stellar halo will allow us (given the development of new CARD–generating dwarf models) to recover the luminosity function of infalling dwarf galaxies — and the detailed accretion history of the halo — across cosmic time.
We present new EAGLE (“Evolution and Assembly of GaLaxies and their Environments”, Schaye et al. 2015) zoom simulations of a range of Milky Way-like galaxies that can uniquely reproduce the metallicities of galactic stars, the ISM, and now the circumgalactic medium (CGM) as probed by quasar absorption line surveys. The surprising result is that the average L* galaxy loses more oxygen to the CGM out to hundreds of kpcs from a galaxy than it retains in its stars. These zooms not only follow the nucleosynthetic yields of 11 elements, they follow the non-equilibrium ionization and cooling of 133 ions, which allow direct comparison to observations of the COS-Halos survey of O VI in galactic halos out to 150 kpc (Tumlinson et al. 2011). The result is a new understanding of the galactic nucleosynthetic yield budget in simulations where galaxies are dramatically shaped by supernovae and black hole feedback. We are now closer to reconciling observed stellar, ISM, and now CGM metallicities with the nucleosynthetic production of the stellar component.
Radial Velocity Experiment (RAVE) observed ~500,000 southern sky stars between 2003 and 2013 in the infra-red calcium triplet (CaII) spectral region. In this study we extended the analysis of RAVE very metal-poor stars ([Fe/H] < −2) presented by Fulbright et al. (2010). We employed a novel method for identifying the metal-poor stars and developed a tool for modeling CaII lines where we also modeled the background noise to avoid systematical biases in the equivalent width (EW) measurements. Final metallicity values were derived with a flexible calibration approach using only 2MASS photometric data and EW measurements obtained from the RAVE spectra.
We examine integrated luminosity relations between the IR continuum and the CO rotational ladder observed for local (ultra) luminous infra-red galaxies ((U)LIRGs, LIR ≥ 1011 M⊙) and normal star forming galaxies in the context of radiation pressure regulated star formation proposed by Andrews & Thompson (2011). This can account for the normalization and linear slopes of the luminosity relations (log LIR = α log L'CO + β) of both low- and high-J CO lines observed for normal galaxies. Super-linear slopes occur for galaxy samples with significantly different dense gas fractions. Local (U)LIRGs are observed to have sub-linear high-J (Jup > 6) slopes or, equivalently, increasing LCOhigh-J/LIR with LIR. In the extreme ISM conditions of local (U)LIRGs, the high-J CO lines no longer trace individual hot spots of star formation (which gave rise to the linear slopes for normal galaxies) but a more widespread warm and dense gas phase mechanically heated by powerful supernovae-driven turbulence and shocks.
Galactic outflows are observed in star-forming galaxies up to high redshift. Still, their physical origins are not well understood, and most simulations fail to reproduce all observed parameters from first principles. With the POGO simulations (Physical Origins of Galactic Outflows), we model AGN and stellar feedback (FB) based on physical assumptions, and investigate their impact on the outflow parameters and on the host-galaxy at very high resolution (1.5 pc). Here, we show that AGN and stellar FB couple non-linearly, and that the mass loading of the resulting outflow highly depends on the mass of the host.
Numerical simulations of star formation faces challenges including the huge spatial dynamic range and the presence of multiply coupled highly non-linear physics, such as magnetic field, supersonic turbulence, gravitation, radiation and protostellar outflow feedback. We present in this symposium our latest high resolution adaptive mesh refinement numerical simulations of the formation of filamentary dark molecular clouds from 4.55 pc size scale down to the formation of a protostellar cluster with maximum resolution at 28 AU. The physical properties of the long braided filamentary dark cloud formed in the simulation, the magnetic field properties of the cloud clumps, and the protostellar mass function in the simulations match well with the latest observations.
We studied the unbiased optical brightness distribution which was calculated from the survival analysis of host galaxies (HGs) data and its relationship with the Swift GRB data of the host galaxies observed by the Keck telescope. Based on the sample obtained from merging the Swift GRB table and the Keck optical data we also studied the dependence of this distribution on the GRB's data. Finally, we compared the HGs distribution with standard galaxies distribution of the DEEP2 redshift survey and checked the result with the VIPERS catalogue too.
It is yet well understood how mass-loss rates from evolved stars depend on metallicities. With a half of the solar metallicity and the distance of only 50 kpc, the evolved stars of the Large Magellanic Cloud (LMC) are an ideal target for studying mass loss at low metallicity. We have obtained spectra of red-supergiants in the LMC, using the Hershel Space Observatory, detecting CO thermal lines fro J=6–5 up to 15–14 lines. Modelling CO lines with non-LTE Radiative transfer code suggests that CO lines intensities can be well explained with high gas-to-dust ratio, with no obvious reduction in mass-loss rate at the LMC. We conclude that the luminosities of the stars are primary factors on mass-loss rates, rather than the metallicity.
A Chandra X-ray Observatory ACIS-I observation and a 6 cm continuum radio observation with the Karl G. Jansky Very Large Array (VLA) together with a multiwavelength study in infrared (2MASS and Spitzer) and optical (USNO-B1.0) shows an increasing surface density of X-ray sources toward the massive protostar. There are at least 43 YSOs within 1.2 pc distance from the massive protostar. This number is consistent with typical B-type stars clusters (Lada & Lada 2003).
We present identification of candidate members of the Beta Pictoris, AB Doradus, and TW Hydrae moving star groups. Our pilot study toward the Kepler field, where a multitude of stellar parameters are available, led to a list of 19 highly probable candidates that share the same range of distance and space (tangential and radial) motion as known members in a moving group. A few candidates lack radial velocity data, but are ROSAT X-ray sources, so are considered as likely young stars.
Core-collapse supernovae (SNe) are the final act in the evolution of stars more massive than about 8–9 solar masses. Determining the progenitors of these explosive events and how massive stars are linked to the different SN types are topics of major significance for several fields of astrophysics. Recent progress in observational techniques now allow for rapid-response spectroscopic observations of SNe within a day of detection Gal-Yam et al. (2014). This allows the study of early phases when the SN shock front has not yet reached spatial scales of 1014 cm. Depending on the progenitor's wind density and SN shock front velocity, these early-time SN observations may probe epochs early enough that the dense parts of the progenitor wind and circumstellar medium (CSM) have not yet been overrun by the SN shock front.
In the developing world astronomy had been treated as the science of elites. As a result of this overwhelming perception, astronomy compared with other applied sciences has got less attention and its role in development has been insignificant. However, the IAU General Assembly decision in 2009 opened new opportunity for countries and professionals to deeply look into Astronomy and its role in development. Then, the subsequent establishment of regional offices in the developing world is helping countries to integrate astronomy with other earth and space based sciences so as to progressively promote its scientific and development importance. Gradually nations have come to know that space is the frontier of tomorrow and the urgency of preeminence on space frontier starts at primary school and ascends to tertiary education. For this to happen, member nations in east African region have placed STEM education at the center of their education system. For instance, Ethiopian has changed University enrollment strategy to be in favor of science and engineering subjects, i.e. every year seventy percent of new University entrants join science and engineering fields while thirty percent social science and humanities. Such bold actions truly promote astronomy to be conceived as gateway to science and technology. To promote the concept of astronomy for development the East African regional office has actually aligned it activities to be in line with the focus areas identified by the IAU strategy (2010 to 2020).
We report on our ongoing project “Statistical studies of HII regions in the nearby extra-galaxies”. We present an overview of our detailed study of warm dust in the nearby Galaxy NGC 4321 (M100), measuring the flux values in the 4 Spitzer-IRAC bands of some 275 HII regions in M100. In addition, we present new measurements of the flux values in the 4 Spitzer-IRAC bands of a complete sample of 70 isolated luminous HII regions in NGC 4736 and 157 regions in NGC 4254. We study the relations between the Hα luminosity and the near-IR luminosity and temperature of HII regions in the three galaxies. We estimate the near-IR luminosities and compare them with the Hα luminosities from archive and literature sources. We find a linear relation between the Hα luminosity and the IRAC luminosity for the HII regions, but no apparent relation between the luminosity and the colour temperature of the regions in any of the three galaxies. The colour temperatures of regions especially in M100 and NGC4254 are confined to a surprisingly narrow range, with a small fraction forming a higher temperature tail to the distribution. These results give new insight into the size function and the 3D distribution of the dust in these regions, and we propose scenarios to explain them.