Astronomical Informant

2022-06-10 04:36:33 arXiv:Carbon-enhanced metal-poor (CEMP) stars are a unique resource for Galactic archaeology because they are closely connected to the First Stars, and/or allow investigating binary interactions at very low metallicity. Comparing the fractions and properties of CEMP stars in different Galactic environments can provide us with unique insights into the formation and evolution of the Milky Way halo and its building blocks. In this work, we investigate whether directly comparing fractions of CEMP stars from different literature samples of very metal-poor ([Fe/H] < -2.0) stars is valid. We compiled published CEMP fractions and samples of Galactic halo stars from the past 25 years, and find that they are not all consistent with each other. Focusing on giant stars, we find significant differences between various surveys when comparing their trends of [Fe/H] versus [C/Fe] and their distributions of CEMP stars. To test the role of the analysis pipelines for low-resolution spectroscopic samples, we re-analysed giant stars from various surveys with the SSPP and FERRE pipelines. We found systematic differences in [C/Fe] of ~0.1-0.4 dex, partly independent of degeneracies with the stellar atmospheric parameters. These systematics are likely due to the different pipeline approaches, different assumptions in the employed synthetic grids, and/or the comparison of different evolutionary phases. We conclude that current biases in (the analysis of) very metal-poor samples limit the conclusions one can draw from comparing different surveys. We provide some recommendations and suggestions that will hopefully aid the community to unlock the full potential of CEMP stars for Galactic archaeology.

via astro-ph updates on arXiv.org https://ift.tt/VcBo1zU Aprire / Come

2022-06-08 16:42:56 Pacific Ocean From the Space Station
http://www.nasa.gov/image-feature/pacific-ocean-from-the-space-station

The International Space Station orbits into a dawn 261 miles above a cloudy Pacific Ocean in this image from April 2022. Aprire / Come

2022-06-08 14:33:42 ATel 15422: Early Optical Spectra of U Sco in Outburst
https://www.astronomerstelegram.org/?read=15422

We obtained optical spectra of U Sco on 2022 June 7.24 and June 8.23 using the 2.4 m Hiltner telescope (+OSMOS) of the MDM Observatory on Kitt Peak and with the 6.5 m MMT (+Blue Channel Spectrograph) on Mount Hopkins. ... Aprire / Come

2022-06-08 05:36:16 arXiv:We study the cosmological information content of the redshift-space galaxy bispectrum monopole at one-loop order in perturbation theory. We incorporate all effects necessary for comparison to data: fourth-order galaxy bias, infrared resummation (accounting for the non-linear evolution of baryon acoustic oscillations), ultraviolet counterterms, non-linear redshift-space distortions, stochastic contributions, projection, and binning effects. The model is implemented using FFTLog, and validated with the PT Challenge suite of $N$-body simulations, whose large volume allows for high-precision tests. Focusing on the mass fluctuation amplitude, $\sigma_8$, and galaxy bias parameters, we find that including one-loop corrections allow us to significantly extend the range of scales over which the bispectrum can be modeled, and greatly tightens constraints on bias parameters. However, this does not lead to noticeable improvements in the $\sigma_8$ errorbar due to the necessary marginalization over a large number of nuisance parameters with conservative priors. Analyzing a BOSS-volume likelihood, we find that the addition of the one-loop bispectrum may lead to improvements on primordial non-Gaussianity constraints by $\lesssim 30\%$ and on $\sigma_8$ by $\approx 10\%$, though we caution that this requires pushing the analysis to short scales where the galaxy bias parameters may not be correctly recovered; this may lead to biases in the recovered parameter values. We conclude that restrictive priors from simulations or higher-order statistics such as the bispectrum multipoles will be needed in order to realize the full information content of the galaxy bispectrum.

via astro-ph updates on arXiv.org https://ift.tt/sq0dyi9 Aprire / Come

2022-06-08 05:36:15 arXiv:We measure homogeneous distances to M31 and 38 associated stellar systems ($-$16.8$\le M_V \le$ $-$6.0), using time-series observations of RR Lyrae stars taken as part of the Hubble Space Telescope Treasury Survey of M31 Satellites. From $>700$ orbits of new/archival ACS imaging, we identify $>4700$ RR Lyrae stars and determine their periods and mean magnitudes to a typical precision of 0.01 days and 0.04 mag. Based on Period-Wesenheit-Metallicity relationships consistent with the Gaia eDR3 distance scale, we uniformly measure heliocentric and M31-centric distances to a typical precision of $\sim20$ kpc (3%) and $\sim10$ kpc (8%), respectively. We revise the 3D structure of the M31 galactic ecosystem and: (i) confirm a highly anisotropic spatial distribution such that $\sim80$% of M31's satellites reside on the near side of M31; this feature is not easily explained by observational effects; (ii) affirm the thin (rms $7-23$ kpc) planar "arc" of satellites that comprises roughly half (15) of the galaxies within 300 kpc from M31; (iii) reassess physical proximity of notable associations such as the NGC 147/185 pair and M33/AND XXII; and (iv) illustrate challenges in tip-of-the-red-giant branch distances for galaxies with $M_V > -9.5$, which can be biased by up to 35%. We emphasize the importance of RR Lyrae for accurate distances to faint galaxies that should be discovered by upcoming facilities (e.g., Rubin Observatory). We provide updated luminosities and sizes for our sample. Our distances will serve as the basis for future investigation of the star formation and orbital histories of the entire known M31 satellite system.

via astro-ph updates on arXiv.org https://ift.tt/3tlhL5b Aprire / Come

2022-06-08 05:36:14 arXiv:Gravitational production of massive particles due to cosmic expansion can be significant during the inflationary and reheating period of the Universe. If the particle also has non-gravitational interactions that do not significantly affect its production, numerous observational probes open up, including cosmological probes. In this work, we focus on the gravitational production of light vector bosons that couple feebly to the Standard Model (SM) particles. Due to the very feeble coupling, the light vector bosons never reach thermal equilibrium, and if the Hubble scale at the end of inflation is above $10^8$ GeV, the gravitational production can overwhelm the thermal production via the freeze-in mechanism by many orders of magnitude. As a result, much stronger constraints from the Big Bang Nucleosynthesis (BBN) can be placed on the lifetime and mass of the vector bosons compared to the scenario where only thermal production is considered. As an example, we study the sub-GeV scale dark photons, which couple to the SM only through kinetic mixing, and derive constraints on the mass and kinetic mixing parameter of the dark photon from the photodisintegration effects on the light element abundances relevant at the end of the BBN when the cosmic age was around $10^4$ s.

via astro-ph updates on arXiv.org https://ift.tt/4qGmrcZ Aprire / Come

2022-06-04 00:47:44 NASA to Highlight Climate Research on Cargo Launch, Sets TV Coverage
http://www.nasa.gov/press-release/nasa-to-highlight-climate-research-on-cargo-launch-sets-tv-coverage

NASA and SpaceX are targeting 10:22 a.m. EDT Friday, June 10, to launch the agency’s next investigation to monitor climate change to the International Space Station. Aprire / Come

2022-06-04 00:40:16 ATel 15413: Spectroscopic classification of transients with the Lick Shane telescope
https://www.astronomerstelegram.org/?read=15413

We report the following classifications from spectroscopic observations with the Kast spectrograph on the Shane telescope obtained on 2022 June 02 UT. ... Aprire / Come

2022-06-03 22:16:16 NASA Announces Winners of 2022 Student Launch Competition
http://www.nasa.gov/press-release/nasa-announces-winners-of-2022-student-launch-competition

For the second year in a row, The University of North Carolina at Charlotte won the launch division, while Tarleton State University in Stephenville, Texas, won first place in the design division of NASA’s 2022 Student Launch rocketry competition. Aprire / Come

2022-06-03 21:15:30 NASA Selects Minority-Serving Institution Proposals to Receive Support
http://www.nasa.gov/feature/jpl/nasa-selects-minority-serving-institution-proposals-to-receive-support

The awardees in the first MSI Space Accelerator have been announced after a competitive application process in which they were encouraged to think like startup businesses. Aprire / Come