1,721,283 research outputs found
Detecting proxima b's atmosphere with JWST targeting CO<sub>2</sub> at 15 μm using a high-pass spectral filtering technique
Get PDFExoplanet Proxima b will be an important laboratory for the search for extraterrestrial life for the decades ahead. Here, we discuss the prospects of detecting carbon dioxide at 15 μm using a spectral filtering technique with the Medium Resolution Spectrograph (MRS) mode of the Mid-Infrared Instrument (MIRI) on the James Webb Space Telescope (JWST). At superior conjunction, the planet is expected to show a contrast of up to 100 ppm with respect to the star. At a spectral resolving power of R = 1790-2640, about 100 spectral CO2 features are visible within the 13.2-15.8 μm (3B) band, which can be combined to boost the planet atmospheric signal by a factor of 3-4, depending on the atmospheric temperature structure and CO2 abundance. If atmospheric conditions are favorable (assuming an Earth-like atmosphere), with this new application to the cross-correlation technique, carbon dioxide can be detected within a few days of JWST observations. However, this can only be achieved if both the instrumental spectral response and the stellar spectrum can be determined to a relative precision of ≤1 10-4 between adjacent spectral channels. Absolute flux calibration is not required, and the method is insensitive to the strong broadband variability of the host star. Precise calibration of the spectral features of the host star may only be attainable by obtaining deep observations of the system during inferior conjunction that serve as a reference. The high-pass filter spectroscopic technique with the MIRI MRS can be tested on warm Jupiters, Neptunes, and super-Earths with significantly higher planet/star contrast ratios than the Proxima system.</p
Reproduction package for the paper "Massive pre-main-sequence stars in M17: Firtst and second overtone CO bandhead emission and the thermal infrared"
No full textThis is a basic reproduction package for the paper "Massive pre-main-sequence stars in M17: First and second overtone CO bandhead emission and the thermal infrared" by J. Poorta et al. 2023. It aims to provide the most important data products and software to check and reproduce the main results of the paper
Concurrent formation of supermassive stars and globular clusters: implications for early self-enrichment
Get PDFWe present a model for the concurrent formation of globular clusters (GCs) and supermassive stars (SMSs, ≳103 M⊙) to address the origin of the HeCNONaMgAl abundance anomalies in GCs. GCs form in converging gas flows and accumulate low-angular momentum gas, which accretes on to protostars. This leads to an adiabatic contraction of the cluster and an increase of the stellar collision rate. A SMS can form via runaway collisions if the cluster reaches sufficiently high density before two-body relaxation halts the contraction. This condition is met if the number of stars ≳106 and the gas accretion rate ≳105 M⊙ Myr−1, reminiscent of GC formation in high gas-density environments, such as – but not restricted to – the early Universe. The strong SMS wind mixes with the inflowing pristine gas, such that the protostars accrete diluted hot-hydrogen burning yields of the SMS. Because of continuous rejuvenation, the amount of processed material liberated by the SMS can be an order of magnitude higher than its maximum mass. This ‘conveyor-belt’ production of hot-hydrogen burning products provides a solution to the mass budget problem that plagues other scenarios. Additionally, the liberated material is mildly enriched in helium and relatively rich in other hot-hydrogen burning products, in agreement with abundances of GCs today. Finally, we find a super-linear scaling between the amount of processed material and cluster mass, providing an explanation for the observed increase of the fraction of processed material with GC mass. We discuss open questions of this new GC enrichment scenario and propose observational tests
Human tissue gene expression TPM values for the advanced forensic biology course
No full textGene expression per tissue: This dataset comes from the Genotype-Tissue Expression (GTEx) database that gathers gene expression data from various human tissues. Specifically, the GTEx Analysis v7 version was used. The file is called "GTEx_Analysis_2016-01-15_v7_RNASeQCv1.1.8_gene_tpm.tsv" and contains tabulated-separated values of median TPM gene expression by tissue (TPM: transcript per million). Genes with a favored sucutaneous-adipose expression profile: This file contains 195 genes that have a statistically (p < 0.01) favored expression profile in subcutaneous adipose tissue compared to other tissues. https://zenodo.org/api/files/7342bbfa-0e4d-49e7-b916-5eff5b638c33/genes_with_a_subcutaneous_adipose_favored_expression.ts
The amazing unity of the Universe: and its origin in the Big Bang
No full textIn the first chapters the author describes how our knowledge of the position of Earth in space and time has developed, thanks to the work of many generations of astronomers and physicists. He discusses how our position in the Galaxy was discovered, and how in 1929, Hubble uncovered the fact that the Universe is expanding, leading to the picture of the Big Bang. He then explains how astronomers have found that the laws of physics that were discovered here on Earth and in the Solar System (the laws of mechanics, gravity, atomic physics, electromagnetism, etc.) are valid throughout the Universe. This is illustrated by the fact that all matter in the Universe consists of atoms of the same chemical elements that we know on Earth. This unity is all the more surprising when one realizes that in the original Big Bang theory, different parts of the Universe could never have communicated with each other. It then is a mystery how they could have shared the same physical laws. This problem was solved by the introduction of the idea of inflation, a phase of extremely rapid expansion of the Universe during the first fraction of a second following the Big Bang. The author explains how the unity of the Universe finds its origin in the Big Bang prior to inflation. The book addresses the many fundamental questions about the Universe and its contents from the perspective of the Big Bang: the formation of structure in the Universe, the questions of the mysterious dark matter and dark energy, the possibilities of other Universes (the Multiverse) and of the existence of intelligent life elsewhere in the Universe
Reproduction Package for the paper "The early evolution of young massive clusters. The kinematic history of NGC6611 / M16"
No full textThis is a comprehensive reproduction package for the paper "The early evolution of young massive clusters. The kinematic history of NGC6611 / M16" by Stoop et al. (2022). This reproduction package aims for open science, with the internal API designation of 'Gold'. This package aims to provide the raw data, and the software and scripts to produce the intermediate and end products. Software and scripts are also available to produce the figures and tables in the paper
Different to the core: The pre-supernova structures of massive single and binary-stripped stars
Get PDFThe majority of massive stars live in binary or multiple systems and will interact with a companion during their lifetimes, which helps to explain the observed diversity of core-collapse supernovae. Donor stars in binary systems can lose most of their hydrogen-rich envelopes through mass transfer. As a result, not only are the surface properties affected, but so is the core structure. However, most calculations of the core-collapse properties of massive stars rely on single-star models. We present a systematic study of the difference between the pre-supernova structures of single stars and stars of the same initial mass (11–21 M⊙) that have been stripped due to stable post-main-sequence mass transfer at solar metallicity. We present the pre-supernova core composition with novel diagrams that give an intuitive representation of the isotope distribution. As shown in previous studies, at the edge of the carbon-oxygen core, the binary-stripped star models contain an extended gradient of carbon, oxygen, and neon. This layer remains until core collapse and is more extended in mass for higher initial stellar masses. It originates from the receding of the convective helium core during core helium burning in binary-stripped stars, which does not occur in single-star models. We find that this same evolutionary phase leads to systematic differences in the final density and nuclear energy generation profiles. Binary-stripped star models have systematically higher total masses of carbon at the moment of core collapse compared to single-star models, which likely results in systematically different supernova yields. In about half of our models, the silicon-burning and oxygen-rich layers merge after core silicon burning. We discuss the implications of our findings for the “explodability”, supernova observations, and nucleosynthesis of these stars. Our models are publicly available and can be readily used as input for detailed supernova simulations
Can a "propelling" disc stay trapped near co-rotation?
Get PDFA strong stellar magnetic field significantly alters the behaviour of an accretion disc around the star. In particular, at low accretion rates it is often assumed that the interaction between the field and the disc will expel the gas out of the disc in an outflow rather than allow it to accrete onto the star – a state known as the “propeller regime". However, recent work has suggested that if the disc is truncated close to the co-rotation radius (where the star’s spin frequency equals the Keplerian frequency of the disc) the disc-field interaction will mostly confine the gas, preventing it from escaping from the disc. The interaction changes the density profile of the disc, and can completely halt accretion onto the star without producing an outflow. In turn, this forces the inner edge of the disc to stay trapped close to the co-rotation radius even when there is no net mass flow through the disc, so that the disc never moves into the true propeller regime. Below I explain how a trapped disc can form and show how this can sometimes result in bursts of accretion onto the star, such as have been observed as low-frequency QPOs in X-ray pulsars SAX J1808.4-3658 and NGC 6440 X- 2. Finally, I discuss how trapped discs could also be responsible for the weak recurrent outbursts seen in NGC 6440 X-2 and IGR J00291+5934
Further Astronomical Fine-tuning of the Old Assyrian and Old Babylonian Chronologies
No full textRecently much progress has been made in the absolute dating of the Old Assyrian and Old Babylonian chronologies by combining a new critical edition of the Old Assyrian eponym lists found at KültepeKaneš (Revised Eponym List) with radiocarbon and astronomical dating techniques. This has led to narrowing down the absolute dating of the Old Babylonian chronology to the two Middle Chronologies (Ammī-ṣaduqa year 1 = 1646 or 1638 BC) and to reducing the candidates for the solar eclipse recorded in the Mari Eponym Chronicle (REL 127) to three eclipses (in 1845 BC, 1838 BC, and 1833 BC). In this paper I use the results of a recent study of the intercalation of the Old Assyrian calendar at Kaneš (REL 81–110) to further refine the absolute dating of the chronology of the first half of the second millennium BC. The new evidence suggests that astronomical intercalation criteria like the heliacal rising of the bright star Sirius may have played an important role in establishing the intercalation pattern of the Old Assyrian calendar. Using the REL to create three different solutions of the Old Assyrian calendar at Kaneš (REL 81–110), one for each candidate solar eclipse, I propose that the observed intercalation pattern provides an additional independent argument in support of the Low Middle Chronology. According to the absolute dating of the Old Assyrian chronology proposed here Šamšī-Adad was born in 1839 BC (REL 126), in the year preceding the partial solar eclipse of 24 March 1838 BC (REL 127) and he died in December 1767 BC (REL 197), during the eighteenth year of the reign of king Hammurabi of Babylon. This chronology proposal implies that the eginning of the reign of the Old Assyrian king Erišum (REL 1) may be dated to 1964 BC
On the Origin of the Lunar and Solar Periods in Babylonian Lunar Theory
No full textIn this investigation, I sketch the way in which Babylonian astronomers may have derived the basic parameters of their lunar theory. I propose that the lunar velocity period of 6247 synodic months which underlies the construction of functions Φ and F of system A is derived by fitting a multiple of the Saros period of 223 synodic months within an integer number of solar years using the 27-year Sirius period relation. I further suggest that the lunar velocity period of 251 synodic months used to construct function F of system B is a direct derivative of the 6247-month period. I also briefly discuss the origin of the periods of the solar velocity function B (of system A) and of the solar longitude function A (of system B) suggesting that the periods of these functions may have been derived from a refined version of the 27-year Sirius period. I finally discuss the timeframe of the possible stepwise development of these early lunar and solar functions
- …
