Observations Of Stars Research Articles

The James Webb Space Telescope Absolute Flux Calibration. III. Mid-infrared Instrument Medium Resolution Integral Field Unit Spectrometer

Abstract We describe the spectrophotometric calibration of the Mid-Infrared Instrument’s (MIRI) Medium Resolution Spectrometer (MRS) aboard the James Webb Space Telescope. This calibration is complicated by a time-dependent evolution in the effective throughput of the MRS; this evolution is strongest at long wavelengths, approximately a factor of 2 at 25 μm over the first 2 yr of the mission. We model and correct for this evolution through regular observations of internal calibration lamps. Pixel flat fields are constructed from observations of the infrared-bright planetary nebula NGC 7027, and photometric aperture corrections from a combination of theoretical models and observations of bright standard stars. We tie the 5–18 μm flux calibration to high signal-to-noise ratio (S/N; ∼600–1000) observations of the O9 V star 10 Lacertae, scaled to the average calibration factor of nine other spectrophotometric standards. We calibrate the 18–28 μm spectral range using a combination of observations of main belt asteroid 515 Athalia and the circumstellar disk around young stellar object SAO 206462. The photometric repeatability is stable to better than 1% in the wavelength range 5–18 μm, and the S/N ratio of the delivered spectra is consistent between bootstrapped measurements, pipeline estimates, and theoretical predictions. The MRS point-source calibration agrees with that of the MIRI imager to within 1% from 7 to 21 μm and is approximately 1% fainter than prior Spitzer observations, while the extended source calibration agrees well with prior Cassini Composite Infrared Spectrometer and Voyager Infrared Interferometer Spectrometer and Radiometer observations.

Photometric Analysis of the Cataclysmic Variable Star LT Eri

Abstract LT Eri is a long-period eclipsing cataclysmic variable star (CV). This study investigates its outbursts, negative superhumps (NSHs), tilted-disk precession, eclipse-depth variations, and observed minus calculated (O – C) behavior, using photometric data from the Transiting Exoplanet Survey Satellite (TESS), the Zwicky Transient Facility, the All-Sky Automated Survey for Supernovae, and the American Association of Variable Star Observers. Our analysis reveals an outburst period of 14.7(31) days, with variable periods ranging from 11.62(4) to 22.15(13) days. Both long and short outbursts were detected, lasting approximately 18 and 10 days, respectively. Analysis of the TESS photometry shows that the NSH period is updated to 0.16265161(7) days, persists during the outburst, and its amplitude is correlated with the outburst phase. A suspected signal of tilted-disk precession with a period of 3.5781(6) days is also detected. Additionally, the eclipse depth shows a periodic variation of 3.6270(9) days, closely matching the tilted-disk precession period; however, no biperiodic variation is found, as seen in the dwarf nova HS 2325+8205, suggesting that this phenomenon is not universal. An O – C analysis reveals a weak oscillation with a period of 3.5772(6) days. Our superposition of sine curves consistent with the NSH period and amplitude, along with mean eclipse curves, produces periodic O – C variations with a period of 3.6666(2) days. This indicates that the observed periodic variations in O – C, often around the disk precession period in CVs, may result from the beat between the NSHs and the eclipse rather than actual variations in the accretion disk.

REsolved ALMA and SMA Observations of Nearby Stars (REASONS)

Context. Planetesimal belts are ubiquitous around nearby stars, and their spatial properties hold crucial information for planetesimal and planet formation models. Aims. We present resolved dust observations of 74 planetary systems as part of the REsolved ALMA and SMA Observations of Nearby Stars (REASONS) survey and archival reanalysis. Methods. We uniformly modelled interferometric visibilities for the entire sample to obtain the basic spatial properties of each belt, and combined these with constraints from multi-wavelength photometry. Results. We report key findings from a first exploration of this legacy dataset: (1) Belt dust masses are depleted over time in a radially dependent way, with dust being depleted faster in smaller belts, as predicted by collisional evolution. (2) Most belts are broad discs rather than narrow rings, with much broader fractional widths than rings in protoplanetary discs. We link broad belts to either unresolved substructure or broad planetesimal discs produced if protoplanetary rings migrate. (3) The vertical aspect ratios (h = H/R) of 24 belts indicate orbital inclinations of ~1–20º, implying relative particle velocities of ~0.1–4 km/s, and no clear evolution of heights with system age. This could be explained by early stirring within the belt by large bodies (with sizes of at least ~140 km to the size of the Moon), by inheritance of inclinations from the protoplanetary disc stage, or by a diversity in evolutionary pathways and gravitational stirring mechanisms. We release the REASONS legacy multidimensional sample of millimetre-resolved belts to the community as a valuable tool for follow-up multi-wavelength observations and population modelling studies.

Geometric Calibration for the Linear Array Camera Based on Star Observation

Geometric Calibration for the Linear Array Camera Based on Star Observation

Binary properties of the globular cluster 47 Tuc (NGC 104)

Spectroscopic observations of binary stars in globular clusters are essential to shed light on the poorly constrained period, eccentricity, and mass ratio distributions and to develop an understanding of the formation of peculiar stellar objects. 47 Tuc (NGC 104) is one of the most massive Galactic globular clusters, with a large population of blue stragglers and with many predicted but as-yet elusive stellar-mass black holes. This makes it an exciting candidate for binary searches. We present a multi-epoch spectroscopic survey of 47 Tuc with the VLT/MUSE integral field spectrograph to determine radial velocity variations for 21 699 stars. We find a total binary fraction in the cluster of (2.4 ± 1.0)%, consistent with previous photometric estimates, and an increased binary fraction among blue straggler stars, approximately three times higher than the cluster average. We find very few binaries with periods below three days, and none with massive dark companions. A comparison with predictions from state-of-the-art models shows that the absence of such short-period binaries and of binaries with massive companions is surprising, highlighting the need to improve our understanding of stellar and dynamical evolution in binary systems.

Examining astrophysical gas cloud collapse using an optical depth-scaled, x-ray-irradiated, carbon-foam sphere

When stellar radiation interacts with a molecular cloud, the cloud's fate depends on the strength of the incident radiation and the radiation's mean-free-path within the cloud [F. Bertoldi, Astrophys. J. 346, 735–755 (1989)]. Under the right conditions, the radiation compresses the cloud and a star formation may occur. Where and when the stellar formation occurs in the cloud's collapse are open questions. Direct observation of the complete star–cloud lifecycle is nearly impossible due to the immense timescales and distances over which the interaction occurs. Laboratory astrophysics offers a way to investigate such a system by scaling the important astrophysical parameters to the laboratory. This work describes laboratory experiments to study the radiation-driven implosion of clouds, using x rays from a laser-irradiated, thin, gold foil as a surrogate star and a carbon-foam sphere as a surrogate cloud. An optically thick system, theoretically corresponding to a star-forming regime, was selected by choice of the foam density. Gold foil and sphere motions were imaged by x-ray radiography. Radiographic images show the formation of an interface between rarefied gold and carbon plasmas, a shock moving into the sphere, and a blunting of the initial sphere's shape. Measurements show that the shock moved linearly around 64 μm/ns into the sphere, and the gold–carbon interface formed by 2 ns at the sphere edge remained stationary. The deformation of the sphere was driven by the incident radiation and not by mechanical pressures applied by gold plasma. The blunting of the sphere was likely due to the geometric reduction of flux near the sphere's poles. Higher x-ray flux near the sphere's equator caused high compression and a faster shock, which flattened the sphere. We will discuss the results and implications of our observations.

Red Stellar Populations and Dust Extinction toward W3

We explore red stellar populations toward the W3 giant molecular cloud through the use of optical-to-infrared (IR) photometry and Gaia DR 3 data, simultaneously characterizing stellar content and properties of dust in the molecular medium. We use a Rayleigh–Jeans color excess method modified to de-redden stellar observations of both red giants (RGs) and OB stars, and construct an IR Hertzsprung–Russell diagram validated against the Besançon Galactic model. Taking advantage of the near-universal IR interstellar extinction law and precise Gaia measurements, we develop a method for obtaining the spectral classification, foreground extinction, and distance moduli of stars, validated by spectroscopically confirmed OB stars. We constrain the observed parallax and proper motion of OB stars in W3, demonstrating the importance of considering systematic effects in the parallax bias, and assign parallax- and proper-motion-based cloud membership to our stellar samples. While it has been assumed that all spectroscopic OB stars are inside the W3 cloud, we find evidence of seven background B stars and three potential runaway OB stars. The methods developed here, which are based on known stellar populations, enable us to identify 82 new OB candidates that are confidently within the cloud. We quantify several dust-to-dust empirical correlations, in particular the IR color excess E(H − [4.5]) and the optical depth τ 1 of submillimeter dust emission at 1 THz using RGs behind W3, measuring a best fit of E(H−[4.5])=(1.07±0.04)×103τ1,HOTT+(0.00±0.02)mag .

Precise Measurements of the LMC Bar’s Geometry with Gaia DR3 and a Novel Solution to Crowding-induced Incompleteness in Star Counting

Abstract We present new measurements of the 2D geometry of the LMC’s stellar bar with precise astrometric observations of red clump stars in Gaia DR3. We develop a novel solution to tackle crowding-induced incompleteness in Gaia data sets with the Gaia BP-RP color excess. Utilizing the color excess information, we derive a 2D completeness map of the LMC’s disk. We find that incompleteness biases the bar measurements and induces large uncertainties. With the completeness-corrected 2D red clump map, we precisely measure the LMC bar’s properties using Fourier decomposition. The bar radius (semimajor axis) is R bar = 2.13 − 0.04 + 0.03 kpc, and its position angle is 121.°26 ± 0.°21. The bar’s strength as quantified by the Fourier bi-symmetric amplitude is S bar = 0.27, indicating that the LMC has a significant bar perturbation. We find the bar has an axis ratio of 0.54 ± 0.03, and is offset with respect to the center of the outer disk isophote at R ≈ 5 kpc by 0.76 ± 0.01 kpc. These LMC bar properties agree with a hydrodynamic model where the SMC has undergone a recent direct collision with the LMC. We compare the LMC’s bar properties with other barred galaxies in the local Universe, and discover that the LMC is similar to other barred galaxies in terms of bar-galaxy scaling relations. We discuss how our completeness correction framework can be applied to other systems in the Local Group.

Navigation in GNSS-Denied Environment Based on Observation of RSOs and Stars

Navigating in an environment, where Global Navigation Satellite System (GNSS) signals are unavailable, presents a formidable challenge. A feasible strategy involves integrating stellar observations with inertial information to realize precise navigation. Inertial/Stellar Celestial Navigation enhances position accuracy by addressing gyro drift through stellar observations. However, the position error still continues to grow over time which arises from unobservable error factors. With improved orbit determination accuracy and the resident space object (RSO) observation method, navigating using RSO observation is gaining viability. This study models the RSO navigation problem as a Perspective-n-Point (PnP) problem and proposes that observing more than 6 RSOs can yield complete solution for position and attitude. Additionally, a tightly coupled navigation algorithm integrating inertial, stellar, and RSO observations is introduced. Simulation validation under dynamic condition demonstrates the algorithm’s efficacy, achieving a position accuracy of 30[Formula: see text]m and an attitude accuracy of 5[Formula: see text]arcsec (RMS) without GNSS data.

The James Webb Space Telescope Absolute Flux Calibration. II. Mid-infrared Instrument Imaging and Coronagraphy

The absolute flux calibration of the Mid-Infrared Instrument imaging and coronagraphy is based on observations of multiple stars taken during the first 2.5 yr of James Webb Space Telescope operations. The observations were designed to ensure that the flux calibration is valid for a range of flux densities, different subarrays, and different types of stars. The flux calibration was measured by combining observed aperture photometry corrected to infinite aperture with predictions based on previous observations and models of stellar atmospheres. A subset of these observations was combined with model point-spread functions to measure the corrections to infinite aperture. Variations in the calibration factor with time, flux density, background level, type of star, subarray, integration time, rate, and well depth were investigated, and the only significant variations were with time and subarray. Observations of the same star taken approximately every month revealed a modest time-dependent response loss seen mainly at the longest wavelengths. This loss is well characterized by a decaying exponential with a time constant of ∼200 days. After correcting for the response loss, the band-dependent scatter around the corrected average (i.e., repeatability) was found to range from 0.1% to 1.2%. Signals in observations taken with different subarrays can be lower by up to 3.4% compared to FULL frame. After correcting for the time and subarray dependencies, the scatter in the calibration factors measured for individual stars ranges from 1% to 4% depending on the band. The formal uncertainties on the flux calibration averaged for all observations are 0.3%–1.0%, with longer-wavelength bands generally having larger uncertainties.

The nuclear symmetry energy and the neutron skin thickness in nuclei

IntroductionWe investigate possible correlations between the stiffness of the symmetry energy at saturation density, the so-called L parameter, and the neutron skin thickness of 48Ca and 208Pb, for which the recent measurements from the CREX and PREX I + II experiments at the Thomas Jefferson Laboratory became available.MethodsWe choose an ensemble of nucleonic equations of state (EoS) derived within microscopic (BHF, Variational, AFDMC) and phenomenological (Skyrme, RMF, DD-RMF) approaches. They are all compatible with the laboratory nuclear collisions data and with current observations of neutron stars (NS) mass and the tidal polarizability of a 1.4 M⊙ NS, as deduced from the GW170817 event.ResultsWe find some degree of correlation between the L parameter and the neutron skin thickness whereas a much weaker correlation does exist with the tidal polarizability and the symmetry energy at saturation density. However, some EoS which are able to explain the CREX experimental data, are not compatible with the PREX I + II data, and viceversa.ConclusionWe confirm the results previously obtained with a different set of EoS models, and find a possible tension between the experimental data and the current understanding of the nuclear EoS.

X-Shooting ULLYSES: Massive stars at low metallicity

On the route toward merging neutron stars and stripped-envelope supernovae, binary population synthesis predicts a large number of post-interaction systems with massive stars that have been stripped of their outer layers. However, observations of such stars in the intermediate-mass regime below the Wolf-Rayet masses are rare. Using X-Shooting ULLYSES (XShootU) data, we have discovered three partially stripped star + Be/Oe binaries in the Magellanic Clouds. We analyzed the UV and optical spectra using the Potsdam Wolf-Rayet (PoWR) model atmosphere code by superimposing model spectra that correspond to each component. The estimated current masses of the partially stripped stars fall within the intermediate-mass range of ≈4 − 8 M⊙. These objects are found to be over-luminous for their corresponding stellar masses, which aligns with the luminosities during core He-burning. Their accompanying Be/Oe secondaries are found to have much higher masses than their stripped primaries (mass ratio ≳2). The surfaces of all three partially stripped stars exhibit clear indications of significant nitrogen enrichment as well as a depletion of carbon and oxygen. Furthermore, one of our sample stars shows signs of substantial helium enrichment. Our study provides the first comprehensive determination of the wind parameters of partially stripped stars in the intermediate-mass range. The wind mass-loss rates of these stars are estimated to be on the order of 10−7 M⊙ yr−1, which is more than ten times higher than that of OB stars with the same luminosity. The current mass-loss recipes commonly employed in evolutionary models to characterize this phase are based on OB or WR mass-loss rates, and they significantly underestimate or overestimate the observed mass-loss rates of (partially) stripped stars by an order of magnitude. Binary evolution models suggest that the observed primaries had initial masses in the range of 12−17 M⊙, and are potential candidates for stripped-envelope supernovae resulting in the formation of a neutron star. If these systems survive the explosion, they will likely evolve to become Be X-ray binaries and later double neutron stars.

Spectroscopic and Photometric Analyses of the Trapezium Stars θ1 Ori A and θ1 Ori D

ABSTRACTIn this paper, we report on the spectroscopic and photometric observations of the two Trapezium stars, Ori A and Ori D. The spectra of these stars were extracted from the ESO and ESPaDOnSarchives. Both stars exhibit nebular emission features, particularly within the core of the Balmer profiles and He I lines at and . Additionally, the spectral energy distributions of these targets were constructed, revealing an infrared excess in both. These emission structures and infrared excesses are attributed to the H II region caused by Ori C. Furthermore, detailed spectroscopic analysis performed to Ori A and Ori D revealed similar abundance patterns, with slight differences in carbon, magnesium, and aluminum. The effective temperatures derived from the spectroscopic analysis were used to determine their positions on the Hertzsprung‐Russell (H‐R) diagram. Additionally, the evolutionary tracks and isochrones constructed on the H‐R diagram allowed for the estimation of their evolutionary masses and ages. Finally, TESS observations of the target stars were obtained to investigate their light variations.

Neutron star collapse from accretion: A probe of massive dark matter particles

We explore the multi-scatter capturing of the massive dark matter (DM) particle inside the neutron star via a momentum-dependent dark matter-nucleon scattering cross-section. We find that the capturing enhanced for the positive velocity and momentum transfer dependent DM-nucleon scattering in comparison with the constant cross-section case. Further, a large capture of the DM particles can be thermalized and lead to black hole formation and, therefore, destroy the neutron star. Using the observation of the old neutron star in the DM-dominated region, we obtain strong constraints on massive DM parameters.

The SDSS-V Local Volume Mapper Telescope System

This paper presents the Local Volume Mapper (LVM) telescope system. LVM is one of three surveys that form the fifth generation of the Sloan Digital Sky Survey (SDSS-V), and it employs a coordinated network of four, 16 cm diameter telescopes feeding integral field units (IFUs) leading to three fiber spectrographs. One telescope hosts the science IFU, while two others observe adjacent fields to calibrate geocoronal emission. The fourth telescope makes rapid observations of bright stars to compensate for telluric absorption. The entrance slits of the spectrographs intersperse the fibers from all three types of telescope, producing truly simultaneous science and calibration exposures. We describe the final design of the telescope system and report on its construction, alignment and testing in the laboratory, as well as the integration, testing, commissioning, and actual on-sky performance at Las Campanas Observatory.

Bayesian evaluation of hadron-quark phase transition models through neutron star observables in light of nuclear and astrophysics data

We investigate the role of hybrid and nucleonic equations of state (EOSs) within neutron star (NS) interiors using Bayesian inference to evaluate their alignment with recent observational data from NICER and LIGO-Virgo (LV) collaborations. We find that smooth hybrid EOSs are slightly favoured in explaining NS mass-radius relations, particularly for pulsars such as PSR J0030+0451 and PSR J0740+6620. However, this preference is not definitive, as gravitational wave (GW) data does not significantly differentiate between our hybrid and nucleonic models. Our analysis also reveals tensions between older NICER data and recent measurements for PSR J0437−4715, highlighting the need for more flexible EOS models. Through two sampling approaches — one fixing the hadronic EOS set and the other without fixing the same, we demonstrate that the hybrid EOS model can incorporate stiffer EOSs, resulting in a better agreement with NICER data but leading to higher tidal deformability, which is less consistent with GW observations. In some recent publications a parameter dc, related to the trace anomaly and its derivative, is used to indicate the presence of deconfined quark matter. We find that our hadronic model, which does not include phase transition to deconfined matter, under the influence of imposed constraints, is able to predict values below 0.2 for dc at around five times saturation density. The hybrid model goes below this threshold at lower densities under the same conditions.

Hamilton Echelle Spectrograph Observations of Solar Analog Field Stars: Lithium Abundance and Activity

We measured lithium (Li) abundance and instantaneous chromospheric Ca ii HK activity in Hamilton Echelle Spectrograph observations of 211 solar analog field stars, with one objective being potential identification of grand minimum candidates for ongoing multiyear observation. At the zero-age main sequence, Li abundance for a typical late-type dwarf begins at the local interstellar medium abundance and over the main sequence lifetime is steadily depleted by convection at a rate dependent on details of the star’s convection and mixing processes. Our Li abundance measurements show an overall decrease in Li abundance with age and effective temperature, consistent with earlier surveys. In our activity measurements, 41 stars show log R′HK ≤ −5.0, which can be considered very inactive. Of the very inactive stars closest to solar effective temperature, 24 show Li abundances within the range typically observed for midlife Sun-like stars. Another three show very low Li abundance, which, combined with the low activity, suggest an older main sequence star or a slightly evolved star. We suggest that the combination of relatively undepleted Li and instantaneous very low activity might make these stars promising candidates for long time-series observations to determine if they are in a grand minimum state. The Hamilton Echelle Spectrograph observations are publicly available for download and are potentially useful for a variety of survey tasks involving Sun-like stars.

Phenomenological model of gravitational self-force enhanced tides in inspiraling binary neutron stars

Gravitational waves from inspiraling binary neutron stars provide unique access to ultradense nuclear matter and offer the ability to constrain the currently unknown neutron star equation-of-state through tidal measurements. This, however, requires the availability of accurate and efficient tidal waveform models. In this paper we present henom, a new phenomenological tidal phase model for the inspiral of neutron stars in the frequency domain, which captures the gravitational self-force informed tidal contributions of the time-domain effective-one-body model esum. henom is highly faithful and computationally efficient, and by choosing a modular approach, it can be used in conjunction with frequency-domain binary black hole waveform model to generate the complete phase for a binary neutron star inspiral. henom is valid for neutron star binaries with unequal masses and mass ratios between 1 and 3, and dimensionless tidal deformabilities up to 5000. Furthermore, henom does not assume universal relations or parametrized equations of state, hence allowing for exotic matter analyses and beyond standard model physics investigations. We demonstrate the efficacy and accuracy of our model through comparisons against esum, numerical relativity waveforms and full Bayesian inference, including a reanalysis of the binary neutron star observation GW170817. Published by the American Physical Society 2024

Probing the Extended Atmospheres of AGB Stars. I. Synthetic Imaging of 1D Hydrodynamical Models at Radio and (Sub-)millimeter Wavelengths

We investigate the observable characteristics of the extended atmospheres of asymptotic giant branch (AGB) stars across a wide range of radio and (sub-)millimeter wavelengths using state-of-the-art 1D dynamical atmosphere and wind models over one pulsation period. We also study the relationships between the observable features and model properties. We further study practical distance ranges for observable sources assuming the capabilities of current and upcoming observatories. We present time-variable, frequency-dependent profiles of pulsating AGB stars’ atmospheres, illustrating observable features in resolved and unresolved observations, including disk brightness temperature, photosphere radius, and resolved and unresolved spectral indices. Notably, temporal variations in disk brightness temperature closely mirror the temperature variability of the stellar atmosphere. We find that while the photospheric radius decreases due to gas dilution in the layers between consecutive shocks, the increase in the observed stellar radius reflects shock propagation through the atmosphere during the expansion phase, providing a direct measurement method for the shock velocity. Furthermore, our models indicate that enhanced gas temperatures after the passage of a strong shock might be observable in the high-frequency Atacama Large Millimeter/submillimeter Array (ALMA) bands as a decrease in the brightness temperature with increasing frequency. We demonstrate that synthetic observations based on state-of-the-art dynamical atmosphere and wind models are necessary for proper interpretations of current (ALMA and Very Large Array (VLA)) and future (Square Kilometre Array and next-generation VLA) observations and that multiwavelength observations of AGB stars are crucial for empirical studies of their extended atmospheres.

Proton ingestion in asymptotic giant branch stars as a possible explanation for J-type stars and AB2 grains

Context. J-type stars are a subclass of carbon stars that are generally Li-rich, not enriched in s-elements, and have low 12C/13C ratios. They were suggested to be the manufacturers of the pre-solar grains of type AB2 (having low 12C/13C and supersolar 14N/15N). Aims. In this Letter, we investigate the possibility that J-type stars are early asymptotic giant branch (AGB) stars that experienced a proton ingestion event (PIE). Methods. We used the stellar evolution code STAREVOL to compute AGB stellar models with initial masses of 1, 2, and 3M⊙ and metallicities [Fe/H] = − 0.5 and 0.0. We included overshooting above the thermal pulse and used a network of 1160 nuclei coupled to the transport equations. The outputs of these models were compared to observations of J-type stars and AB2 grains. Results. In solar-metallicity AGB stars, PIEs can be triggered if a sufficiently high overshoot is considered. These events lead to low 12C/13C ratios, high Li abundances, and no enrichment in s-elements. We find that the 2 − 3 M⊙ AGB models experiencing a PIE can account for most of the observational features of J-type stars and AB2 grains. The remaining tensions between models and observations are (1) the low 14N/15N ratio of some AB2 grains and of 2 out of 13 J-type stars, (2) the high 26Al/27Al of some AB2 grains, and (3) the J-type stars with A(Li) < 2. Extra mixing mechanisms can alleviate some of these tensions, such as thermohaline or rotation. Conclusions. This work highlights a possible match between AGB stellar models that undergo a PIE and J-type stars and AB2 grains. To account for other types of carbon stars, such as N-type stars, PIEs should only develop in a fraction of solar-metallicity AGB stars. Additional work is needed to assess how the occurrence of PIEs depends on mixing parameters and initial conditions, and therefore to further confirm or exclude the proposed scenario.