Hasil untuk "Astronomy"

T. Kippenberg, Ronald Holzwarth, Scott A. Diddams

M. Uslenghi, Isabella Pagano, C. Pontoni et al.

This paper reports on the current status of the World Space Observatory WSO-UV, a space mission for UV astronomy, planned for launch at the beginning of next decade. It is based on a 1.7 m telescope, with focal plane instruments including high resolution spectrographs, long slit low resolution spectrographs and imaging cameras.

D. Tody

G. Nason, Bernard Walter Silverman

R. Vera

C. R. Nugent, K. P. Andersen, James M. Bauer et al.

Near-Earth objects (NEOs) have the potential to cause extensive damage and loss of life on Earth. Advancements in NEO discovery, trajectory prediction, and deflection technology indicate that an impact could be prevented, with sufficient warning time. We derive an impact frequency of NEOs 140 m and larger, using the NEOMOD2 NEO population model and JPL Horizons . We then place that frequency in context with other preventable causes of death, allowing for comparison between a planet-wide event and individual events that cause fatalities such as car crashes and carbon monoxide poisoning. We find that the chance of a >140 m asteroid hitting the Earth is more likely than the chance of an individual being struck by lightning.

Yongyun Chen, Qiusheng Gu, Junhui Fan et al.

Accretion supermassive black holes in the center of active galaxies usually produce “jet”-collimated bipolar outflows of relativistic particles. Magnetic fields near the black hole event horizon may play a crucial role in the formation of jets/outflows. Both theory and observation indicate that jets/outflows driven by centrally active supermassive black holes have a feedback effect on the overall properties of the host galaxies. Therefore, the magnetic field is a key ingredient for the formation and evolution of galaxies. Here, we report a clear correlation between the magnetic field of jets and star formation rate for a large sample of 96 galaxies hosting supermassive black holes, which suggests that the star formation of active galactic nuclei host galaxies may be powered by the jets.

Douglas Grion Filho, Puragra Guhathakurta, Stanley M. Rinehart V et al.

The recent discovery that red supergiants in M31 and M33 contain a weak CN spectral absorption feature at ​​​​​​∼8000 Å prompted us to analyze a large CTIO 4 m Hydra spectral database of stars in the Large Magellanic Cloud (LMC). We find 751 confirmed weak CN stars in the LMC, present an overview of their spectral and photometric properties, and compare them with the weak CN stars in M31 and M33. We use a method for automatically identifying weak CN stars based on a spectral template and find that weak CN stars are almost exclusively short-lived massive stars in the core He-burning evolutionary phase. We derive a mean main-sequence age of 40 Myr for these stars through a Bayesian approach to isochrone fitting that is consistent across all three galaxies. We then examine possible evolutionary processes and atmospheric conditions that could lead to weak CN stars using a suite of low-resolution model spectra. We find a preferred range of values for T _eff and log g in O-rich stars that would result in the CN absorption and also speculate that this feature could arise due to the N enhancement expected in fast-rotating stars, though more targeted modeling is required.

R. Abbasi, M. Ackermann, J. Adams et al.

Hao Li, Tanausú del Pino Alemán, Javier Trujillo Bueno et al.

We study the circular polarization of the magnetic-field-induced transition (MIT) between the 3 d ^5 ( ^6 S )4 d ^7 D _2 and 3 d ^5 ( ^6 S )4 p ^7 P _4 ° states of Cr i at 533.03 nm (wavelength in air). The fractional circular polarization V / I of this spectral line resulting from the solution of the radiation transfer problem in a sunspot model permeated by a homogeneous magnetic field of 3 kG shows amplitudes of about 2%. Spectropolarimetric observations of two sunspots were obtained with the Zurich Imaging Polarimeter-3 at the Istituto ricerche solari Aldo e Cele Daccò observatory in Locarno, Switzerland. The observed V / I profiles show approximately antisymmetrical shapes with an amplitude of around 0.1% and 0.2% for the two sunspots. The center of this profile coincides with the wavelengths predicted for the abovementioned MIT. We apply an inversion code to the spectropolarimetric data of the Cr i -permitted lines at 532.91 and 532.98 nm, as well as to the MIT line at 533.03 nm, to infer a stratification of the emitting atmosphere. We compare the V / I profiles synthesized in the inferred atmosphere models with the observations, showing that the observed signal likely corresponds to the MIT line.

Iryna Chemerynska, Hakim Atek, Pratika Dayal et al.

The mass–metallicity relation provides crucial insights into the baryon cycle in galaxies and strong constraints on galaxy formation models. We use JWST NIRSpec observations from the UNCOVER program to measure the gas-phase metallicity in a sample of eight galaxies during the epoch of reionization at z = 6–8. Thanks to the strong lensing of the galaxy cluster Abell 2744, we are able to probe extremely low stellar masses between 10 ^6 and 10 ^8 M _⊙ . Using strong-line diagnostics and the most recent JWST calibrations, we derive extremely low oxygen abundances in the range of 12 + log(O/H) = 6.7–7.8. By combining this sample with more massive galaxies at similar redshifts, we derive a best-fit relation of 12 + log(O/H) = $-{0.076}_{-0.03}^{+0.03}\times {(\mathrm{log}({M}_{\star }))}^{2}+{1.61}_{-0.52}^{+0.52}$ × $\mathrm{log}({M}_{\star })-{0.26}_{-0.10}^{+0.10}$ , which becomes steeper than determinations at z ∼ 3–6 toward low-mass galaxies. Our results show a clear redshift evolution in the overall normalization of the relation, galaxies at higher redshift having significantly lower metallicities at a given mass. A comparison with theoretical models provides important constraints on which physical processes, such as metal mixing, star formation or feedback recipes, are important in reproducing the observations. Additionally, these galaxies exhibit star formation rates that are higher by a factor of a few to tens compared to extrapolated relations at similar redshifts or theoretical predictions of main-sequence galaxies, pointing to a recent burst of star formation. All these observations are indicative of the highly stochastic star formation and interstellar medium enrichment expected in these low-mass systems, suggesting that feedback mechanisms in high- z dwarf galaxies might be different from those in place at higher masses.

Barry F. Madore, Wendy L. Freedman

Using an updated and significantly augmented sample of Cepheid and tip of the red giant branch (TRGB) distances to 28 nearby spiral and irregular galaxies, covering a wide range of metallicities, we have searched for evidence of a correlation of the zero-point of the Cepheid period–luminosity relation with H ii region (gas-phase) metallicities. Our analysis, for the 21 galaxies closer than 12.5 Mpc, results in the following conclusions: (1) The zero-points of the Cepheid and TRGB distance scales are in remarkably good agreement, with the mean offset in the zero-points of the most nearby distance-selected sample being close to zero, Δ μ _o (Cepheid—TRGB) = −0.026 ± 0.015 mag (for an I -band TRGB zero-point of M _I = −4.05 mag); however, for the more distant sample, there is a larger offset between the two distance scales, amounting to −0.073 ± 0.057 mag 〈Δ μ _o 〉 (Cepheids—TRGB) = −0.026 ± 0.015 mag, for an I -band TRGB zero-point of M _I = −4.05 mag. (2) The individual differences, about that mean, have a measured scatter of ±0.068 mag. (3) We find no statistically significant evidence for a metallicity dependence in the Cepheid distance scale using the reddening-free W ( V , VI ) period–luminosity relation: Δ μ _o ( Cepheid − TRGB ) = − 0.022( ± 0.015) × ([O/H] − 8.50) − 0.003(±0.007).

Benjamin M. Bolker

Information-theoretic (IT) and multi-model averaging (MMA) statistical approaches are widely used but suboptimal tools for pursuing a multifactorial approach (also known as the method of multiple working hypotheses) in ecology. (1) Conceptually, IT encourages ecologists to perform tests on sets of artificially simplified models. (2) MMA improves on IT model selection by implementing a simple form of shrinkage estimation (a way to make accurate predictions from a model with many parameters relative to the amount of data, by “shrinking” parameter estimates toward zero). However, other shrinkage estimators such as penalized regression or Bayesian hierarchical models with regularizing priors are more computationally efficient and better supported theoretically. (3) In general, the procedures for extracting confidence intervals from MMA are overconfident, providing overly narrow intervals. If researchers want to use limited data sets to accurately estimate the strength of multiple competing ecological processes along with reliable confidence intervals, the current best approach is to use full (maximal) statistical models (possibly with Bayesian priors) after making principled, a priori decisions about model complexity.

Kazuhiro Sekiguchi, Jess McIver, Annapurni Subramaniam et al.

Policy Brief on "Regional and Global Collaborations in Astronomy", distilled from the corresponding panel that was part of the discussions during S20 Policy Webinar on Astroinformatics for Sustainable Development held on 6-7 July 2023. Astronomy brings together advanced scientific research, state-of-the-art technology, and educational initiatives, all while captivating and stimulating people of all ages. By doing so, it possesses the potential to serve as a powerful catalyst for sustainable global development and the resolution of global societal issues. It attracts a diverse range of scientists and experts from various fields, fostering collaboration and innovation. By leveraging their resources, influence, and diplomatic initiatives, S20 academies can foster an enabling environment for international collaborations in astronomy, facilitate knowledge exchange, and drive scientific advancements that benefit humanity. This policy brief explores the opportunities and challenges presented by regional and global collaborations in astronomy. The policy webinar took place during the G20 presidency in India (2023). A summary based on the seven panels can be found here: arxiv:2401.04623.

Moire K. M. Prescott, Laura Madson, Sandra M. Way et al.

While many previous studies have indicated that encouraging a growth mindset can improve student learning outcomes, this conclusion's applicability to college-level astronomy classrooms remains poorly understood owing to the variation in students' overall and domain-specific learning attitudes. To address this, we surveyed undergraduate students in an introductory astronomy class about their attitudes towards learning astronomy over the course of five semesters. Overall, students felt an affinity for astronomy, felt moderately competent, perceived astronomy to be intermediate in terms of difficulty, and agreed strongly with standard statements reflecting a "growth mindset," i.e., the belief that intelligence is malleable rather than fixed from birth. Their responses were stable over the course of the semester and did not appear to depend strongly on student demographics. The unexpected start of the COVID-19 pandemic and the associated shift to all-virtual learning correlated with a drop in their affinity for astronomy, a small decrease in their perceived competence, and an increase in the perceived difficulty of the topic. Their overall learning mindset showed negligible change during this time, emphasizing the stability of their belief in a growth mindset as compared to other measured learning attitudes. However, more nuanced questions about their behaviors and interpretations in the classroom, about how they felt "in the moment", and about what factors were most important for their success in the class revealed significantly lower alignment with a growth mindset. This suggests that while introductory astronomy students may believe that they have a growth mindset, this mindset is not necessarily reflected in their self-reported classroom behaviors or measured responses to actual learning challenges.

Stefan Andersson, Stefan Andersson, David Gobrecht et al.

Reactions of SiO molecules have been postulated to initiate efficient formation of silicate dust particles in outflows around dying (AGB) stars. Both OH radicals and H2O molecules can be present in these environments and their reactions with SiO and the smallest SiO cluster, Si2O2, affect the efficiency of eventual dust formation. Rate coefficients of gas-phase oxidation and clustering reactions of SiO, Si2O2 and Si2O3 have been calculated using master equation calculations based on density functional theory calculations. The calculations show that the reactions involving OH are fast. Reactions involving H2O are not efficient routes to oxidation but may under the right conditions lead to hydroxylated species. The reaction of Si2O2 with H2O, which has been suggested as efficient producing Si2O3, is therefore not as efficient as previously thought. If H2O molecules dissociate to form OH radicals, oxidation of SiO and dust formation could be accelerated. Kinetics simulations of oxygen-rich circumstellar environments using our proposed reaction scheme suggest that under typical conditions only small amounts of SiO2 and Si2O2 are formed and that most of the silicon remains as molecular SiO.

Li Wang, Chengyuan Li, Long Wang et al.

The detection of split main sequences (MSs) associated with young clusters (≲600 Myr) has attracted a lot of attention. A prevailing scenario is that a bimodality of stellar rotation distribution drives the bifurcation of the MS. Nevertheless, the origin of the stellar rotation dichotomy remains unclear. Hypotheses involving tidally locked binaries or blue straggler stars (BSSs) have been proposed to explain the observed split MSs. This work examines if the long-term dynamical evolution of star clusters can produce the observed split MSs, through high-performance N -body simulation. For example, the young massive cluster NGC 1856 exhibits an apparent MS bifurcation. Our simulation reports that at the age of NGC 1856, tidally locked binaries are fully mixed with single stars. This is consistent with the observation that there is no significant spatial difference between blue MS and red MS stars. However, we find that only high-mass-ratio binaries can evolve to the tidally locked phase at the age of the NGC 1856. These tidally locked binaries will populate a much redder sequence than the MS of single stars rather than a blue MS, which is inconsistent with the hypothesis. The number of tidally locked binaries cannot account for the observation. Our simulation shows that BSSs produced by binary interactions do populate in the blue periphery as shown in a color–magnitude diagram, and their spatial distribution shows a similar pattern of single stars. However, the number of BSSs does not fit the observation.

Zachary Richards, Angela M. Kelly

The present study examined demographic and academic predictors of astronomy performance of community college students enrolled in astronomy courses in a large suburban community college. The theoretical framework was based upon a deconstructive approach for predicting community college performance whereby students academic pathways through higher education institutions are examined to understand their dynamic interaction with institutional integration and progress towards academic goals. Transcript data analysis was employed to elicit student demographics and longitudinal academic coursework and performance. A logistic regression model was generated to identify significant predictors of astronomy performance which included mathematics achievement enrollment in remedial mathematics and enrollment in multiple astronomy courses. The results imply a greater focus on mathematics preparation and performance may mediate astronomy outcomes for community college students. Notably demographic variables including ethnicity socioeconomic status gender and age were not significant predictors of astronomy performance in the multivariable model suggesting the course is a potential gateway for diversifying STEM access. Also astronomy interest as measured by enrollment in multiple astronomy courses was related to performance. Further implications for practice are discussed.

Erik Høg

Information on archives from the 1950s of 15 astronomical observatories is provided beginning with a list of correspondence and other information related to astronomy of the Copenhagen University Observatory in the 1950s. The Appendix contains information from the 14 other observatories about their archives from those years, most of them having no archive at all. Public links are given to most of the files. - Print of the present list and the Danish astronomy archive itself will be placed at the Rigsarkivet, the Danish National Archives.

Rachel Freed, David McKinnon, Michael Fitzgerald et al.

This paper presents a new astronomy self efficacy instrument, composed of two factors, one relating to learning astronomy content, which we call astronomy personal self efficacy, and the other relating to the use of astronomical instrumentation, specifically the use of remote robotic telescopes for data collection. The latter is referred to as the astronomy instrumental self efficacy factor. The instrument has been tested for reliability and construct validity. Reliability testing showed that factor 1 had a Cronbachs alpha of 0.901 and factor 2 had a Cronbachs alpha of 0.937. Construct validity was established by computing one way analyses of variances, with the p value suitably protected, using independent variables peripherally related to the constructs. These analyses demonstrate that both scales possess high construct validity. The development of this astronomy specific instrument is an important step in evaluating self efficacy as a precursor to investigating the construct of science identity in the field of astronomy.