Spectrophotometric Observations Research Articles

Polarimetric monitoring of primitive asteroids near perihelion in order to detect their sublimation-dust activity

UBVR polarimetric observations of 12 main-belt mostly primitive asteroids located near perihelion heliocentric distances were carried out from December 2022 to April 2023 with Zeiss-2000 telescope at the Terskol Peak observatory. The purpose of the monitoring program wasto search for changes in the polarimetric parameters of the asteroids caused by possible sublimation-dust activity, as a result of which the formation of rarefied dust exospheres of asteroids is possible. The objects of the program were asteroids: (1) Ceres, (53) Kalypso, (117) Lomia, (164) Eva, (214) Ashera, (324) Bamberga, (419) Aurelia, (505) Cava, (554) Peraga, (654) Zelinda, (704) Interamnia, (1021) Flammario. Polarimetric observations of asteroids (117) Lomia, (164) Eva and (505) Kava were made for the first time, the remaining asteroids were observed earlier. Only for two asteroids (1) Ceres and (704) Interamnia, according to spectrophotometric observations, temporal spectrophotometric variability was noted earlier. Analysis of temporal changes in the degree of polarization of asteroids and comparison of the results of observations with the data available in the literature showed that the stability of the observed degree of polarization is comparable with measurement errors of ~(0.02–0.1)% for asteroids of different brightness. Thus, during the observation period, no noticeable polarization signs of temporary sublimation-dust activity of the observed asteroids were detected. Additionally, it is shown that the currently existing variants of the spectral taxonomy of asteroids, based on spectrophotometric data and albedo, demonstrate a significant scattering of the selected classes when compared with their polarimetric phase dependencies.The asteroid (554) Peraga has been confirmed to have a negative degree of polarization at angles less than the inversion angle. Measurements of the polarization of the asteroid (1) Ceres in a wide range of wavelengths did not confirm the previously suspected change in the angle of the polarization plane with the wavelength.

Modeling the spectral energy distribution of starburst galaxies

Context. Analyzing multiwavelength observations of galaxies from the far-ultraviolet to the millimeter domains provides a wealth of information on the physical properties of galaxies and their evolution across cosmic time. Existing or upcoming ground-based or space-borne facilities with enhanced sensitivities and resolutions open an unprecedented window on the galaxy evolution in the early Universe. However, the derivation of galaxy properties from nebular emission lines is not trivial because the interstellar medium in a galaxy may be patchy, and emission might originate both from starburst emission regions and from partially covered photon-dominated regions. Aims. We model both the nebular continuum emission and the line emission of the spectral energy distribution for galaxies exhibiting both a HII region-like emission and emission like that from a photon-dominated regions to account for the partial shielding of the starburst emission region by dense clouds. Methods. Nebular galactic emission was modeled from far-ultraviolet to millimeter ranges in a two-sector model with an HII region and a photon-dominated region. The partial overlap of the HII region by the photon-dominated region was accounted for by a covering factor. We generated grids of emission spectra using the Cloudy photoionization code for our two-sector model. Results. We compared our models with spectral lines from different samples of galaxies for which we mixed characteristic emission from starburst regions and denser regions. We show that the infrared line ratios can constrain the density, metallicity, photoionization parameter, and the covering factor. We also built infrared diagnostic diagrams based on different infrared line ratios in which the galaxy location contains information about its physical conditions. Conclusions. The two-sector model that couples starburst emission regions and photon-dominated regions can span the existing observations. We implement the resulting emission line libraries in the CIGALE galaxy spectral energy distribution code to help interpret spectrophotometric observations.

Amino acid profile, Antioxidant Activity and flavonoid Content of White Lotus ‘Purain’ from North Bihar, India

India's national flower is the lotus. A lot of seed is carried by white lotuses. Protein and other bioactive substances are abundant in white lotus seeds. An experiment was carried out at the ICAR-National Research Centre in Makhana in 2023-24 to assess the nutritional quality and anti-oxidant characteristics of white lotus seed, which is abundant during the rainy and autumn seasons in the wetland ecosystem of north Bihar. Seeds of white purain accession were grinded and its flour chemically analyzed using AOAC standard methods. Estimation of amino acids was based on the reaction of free amino acids with phenyl isothiocyanate produces stable derivatives that are then separated using liquid chromatography. Anti-oxidant activities were estimated in spectrophotometric observation by DPPH and FRAP methods, based on electron transfer reactions, which visually results on the reduction of a coloured oxidant. Flavonoids are estimated by UHPLC methods. The white lotus purain seed content 17.8±054 % protein, 1.09±0.07 % fat and 1.94±0.08 % crude fibre. The nutritional study also revealed that the appreciable amount of arginine (12.70 g/kg ) and histidine (3.62 g/kg ) were present in the protein of the dry endosperm of Nelumbium spp. In addition, the lotus seed endosperm has a fair source of quercetin (422.0µg/kg) and kaempferol (200.0 µg/kg) as pure flavonoids which influence the rapid glucose metabolism in human cell. The greatest DPPH and FRAP values were found in seed endosperm of white lotus purain, which had 988.05±2.25 mg AEAC/100g FW and 461.78±1.79 mg AEAC/100g FW, respectively.

Non-LTE abundance analysis of A-B stars with low rotational velocities – II. Do A-B stars with normal abundances exist?

ABSTRACT We present chemical composition and fundamental parameters (the effective temperature, surface gravity, and radius) for four sharp-lined A-type stars γ Gem (HD 41705), o Peg (HD 214994), θ Vir (HD 114330), and ν Cap (HD 193432). Our analysis is based on a self-consistent model fitting of high-resolution spectra and spectrophotometric observations over a wide wavelength range. We refined the fundamental parameters of the stars with the sme (Spectroscopy Made Easy) package and verified their accuracy by comparing with the spectral energy distribution and hydrogen line profiles. We found Teff/log g = 9190 ± 130 K/3.56 ± 0.08, 9600 ± 50 K/3.81 ± 0.04, 9600 ± 140 K/3.61 ± 0.12, and 10200 ± 220 K/3.88 ± 0.08 for γ Gem, o Peg, θ Vir, and ν Cap, respectively. Our detailed abundance analysis employs a hybrid technique for spectrum synthesis based on classical model atmospheres calculated in local thermodynamic equilibrium (LTE) assumption together with the non-LTE (NLTE) line formation for 18 of 26 investigated species. Comparison of the abundance patterns observed in A stars of different types (normal A, Am, and Ap) with similar fundamental parameters reveals significant abundance diversity that cannot be explained by the current mechanisms of abundance peculiarity formation in stellar atmospheres. We found a rise of the heavy element (Zn, Sr, Y, Zr, and Ba) abundance excess up to +1 dex with Teff increasing from 7200 to 10 000 K, with a further decrease down to solar value at Teff = 13 000 K, indicating that stars with solar element abundances can be found among late B-type stars.

A novel technique for studying the effects of technologically processed antibodies by evaluating the rate of oxidation of ascorbic acid during the reduction of the green–blue ABTS + radical

Since the pharmaceutical market is developing, there is a need for novel techniques for determining the physical–chemical properties of drug solutions. Drugs based on technologically processed antibodies (TPA) are an example of compounds that require a methodology for studying their effects. It has been shown that the process of external impacts during the manufacture of TPA-based drugs can induce breaking of intermolecular and intramolecular bonds in the solvent molecules, providing the emergence of new bonds with the molecules of the substance used for the manufacture of an active pharmaceutical ingredient. This article focuses on the technique applied for assessing the mentioned effect of TPA and consists in spectrophotometric observation of the oxidation process of ascorbic acid (AA) in the solution. The amount of oxidized AA was detected using ABTS·+(2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radical-cation, which, when interacting with AA, is reduced and changes the color from green-blue to colorless. This technique showed the reproducibility of statistically significant differences in the amount of oxidized AA in the presence of TPA compared to controls and can be used to detect the changes in the properties of solutions exposed to the effect of the TPA samples.

Physical parameters of stellar population in star formation regions of galaxies

ABSTRACT We present the results of a study of young unresolved stellar groupings (clusters, OB associations, and their complexes) associated with H ii regions, based on the coupling of spectroscopic, photometric and H α spectrophotometric observations of star formation regions. Along with our own observations, we use a part of the spectroscopic and H α data from the literature and open data bases. The study is based on the catalogue of 1510 star formation regions with ages ∼10–20 Myr in 19 spiral galaxies, compiled by us earlier. We study the morphology of stellar groupings and their relation with the associated H α emission region. Extinctions, gas chemical abundances, and sizes of star formation regions are measured. Using numerical simple stellar population models computed for metallicities fixed from observations to intrinsic colours of the studied star formation regions, we estimated ages and masses of stellar population of 400 young stellar groupings. Different relations between observational and physical parameters of the young stellar population in star formation regions are discussed.

Detector bandwidth and polarization switching rates: spectrophotometric observations of the Sun by the Birmingham Solar Oscillations Network

Abstract The Birmingham Solar Oscillations Network (BiSON) observes acoustic oscillations of the Sun. The dominant noise source is caused by fluctuations of Earth’s atmosphere, and BiSON seeks to mitigate this effect by combining multiple rapid observations in alternating polarization states. Current instrumentation uses bespoke Pockels-effect cells to select the polarization state. Here, we investigate an alternative off-the-shelf solution, a liquid crystal (LC) retarder, and discuss the potential impact of differences in performance. We show through electrical simulation of the photodiode-based detectors, and assessment of both types of polarization device, that although the switching rate is slower the off-the-shelf LC retarder is a viable replacement for a bespoke Pockels-effect cell. The simplifications arising from the use of off-the-shelf components allow easier and quicker instrumentation deployment.

The Spectroscopic Classification of Astronomical Transients (SCAT) Survey: Overview, Pipeline Description, Initial Results, and Future Plans

We present the Spectroscopic Classification of Astronomical Transients (SCAT) survey, which is dedicated to spectrophotometric observations of transient objects such as supernovae and tidal disruption events. SCAT uses the SuperNova Integral-Field Spectrograph (SNIFS) on the University of Hawai’i 2.2 m (UH2.2m) telescope. SNIFS was designed specifically for accurate transient spectrophotometry, including absolute flux calibration and host-galaxy removal. We describe the data reduction and calibration pipeline including spectral extraction, telluric correction, atmospheric characterization, nightly photometricity, and spectrophotometric precision. We achieve ≲5% spectrophotometry across the full optical wavelength range (3500–9000 Å) under photometric conditions. The inclusion of photometry from the SNIFS multi-filter mosaic imager allows for decent spectrophotometric calibration (10%–20%) even under unfavorable weather/atmospheric conditions. SCAT obtained ≈640 spectra of transients over the first 3 yr of operations, including supernovae of all types, active galactic nuclei, cataclysmic variables, and rare transients such as superluminous supernovae and tidal disruption events. These observations will provide the community with benchmark spectrophotometry to constrain the next generation of hydrodynamic and radiative transfer models.

Spectral Evolution of Dark Asteroid Surfaces Induced by Space Weathering over a Decade

The surfaces of airless bodies like asteroids in the solar system are known to be affected by space weathering. Experiments simulating space weathering are essential for studying the effects of this process on meteorite samples, but the problem is that the time spent to reproduce space weathering in these experiments is billions of times shorter than the actual phenomenon. In 2010 December, the T-type asteroid 596 Scheila underwent a collision with an impactor a few tens of meters in size. A decade later, there is an opportunity to study how the surface layer of this asteroid is being altered by space weathering after the impact. To do so, we performed visible spectrophotometric and near-infrared spectroscopic observations of 596 Scheila. The acquired spectrum is consistent with those observed shortly after the 2010 impact event within the observational uncertainty range. This indicates that the surface color of dark asteroids is not noticeably changed by space weathering over a 10 yr period. This study is the first to investigate color changes due to space weathering on an actual asteroid surface in the solar system. Considering that fresh layers are regularly created on asteroid surfaces by collisions, we suggest a genetic link between D/T-type and dark (low albedo) X-complex asteroids and very red objects such as 269 Justitia, 732 Tjilaki, and 203 Pompeja. New observations show that 203 Pompeja has an X-type-like surface, with some local surface areas exhibiting a very red spectrum.

The Dawn of Disk Formation in a Milky Way-sized Galaxy Halo: Thin Stellar Disks at z > 4

Abstract We present results from GigaEris, a cosmological, N-body hydrodynamical “zoom-in” simulation of the formation of a Milky Way-sized galaxy halo with unprecedented resolution, encompassing of order a billion particles within the refined region. The simulation employs a modern implementation of smoothed-particle hydrodynamics, including metal-line cooling and metal and thermal diffusion. We focus on the early assembly of the galaxy, down to redshift z = 4.4. The simulated galaxy has properties consistent with extrapolations of the main sequence of star-forming galaxies to higher redshifts and levels off to a star formation rate of ∼60 M ⊙ yr−1 at z = 4.4. A compact, thin rotating stellar disk with properties analogous to those of low-redshift systems arises already at z ∼ 8. The galaxy rapidly develops a multi-component structure, and the disk, at least at these early stages, does not grow “upside-down” as often reported in the literature. Rather, at any given time, newly born stars contribute to sustain a thin disk. The kinematics reflect the early, ubiquitous presence of a thin disk, as a stellar disk component with v ϕ /σ R larger than unity is already present at z ∼ 9–10. Our results suggest that high-resolution spectro-photometric observations of very high-redshift galaxies should find thin rotating disks, consistent with the recent discovery of cold rotating gas disks by ALMA. Finally, we present synthetic images for the James Webb Space Telescope NIRCam camera, showing how the early disk would be easily detectable already at those early times.

Taxonomy of Asteroids From the Legacy Survey of Space and Time Using Neural Networks

The Legacy Survey of Space and Time (LSST) is one of the ongoing or future surveys, together with the Gaia and Euclid missions, which will produce a wealth of spectrophotometric observations of asteroids. This article shows how deep learning techniques with neural networks can be used to classify the upcoming observations, particularly from LSST, into the Bus-DeMeo taxonomic system. We report here a success ratio in classification up to 90.1% with a reduced set of Bus-DeMeo types for simulated observations using the LSST photometric filters. The scope of this work is to introduce tools to link future observations into existing Bus-DeMeo taxonomy.

A new method to measure the spectra of transiting exoplanet atmospheres using multi-object spectroscopy

ABSTRACT Traditionally, ground-based spectrophotometric observations probing transiting exoplanet atmospheres have employed a linear map between comparison and target star light curves (e.g. via differential spectrophotometry) to correct for systematics contaminating the transit signal. As an alternative to this conventional method, we introduce a new Gaussian Processes (GP) regression-based method to analyse ground-based spectrophotometric data. Our new method allows for a generalized non-linear mapping between the target transit light curves and the time-series used to detrend them. This represents an improvement compared to previous studies because the target and comparison star fluxes are affected by different telluric and instrumental systematics, which are complex and non-linear. We apply our method to six Gemini/GMOS transits of the warm (Teq = 990 K) Neptune HAT-P-26b. We obtain on average ∼20 per cent better transit depth precision and residual scatter on the white light curve compared to the conventional method when using the comparison star light curve as a GP regressor and ∼20 per cent worse when explicitly not using the comparison star. Ultimately, with only a cost of 30 per cent precision on the transmission spectra, our method overcomes the necessity of using comparison stars in the instrument field of view, which has been one of the limiting factors for ground-based observations of the atmospheres of exoplanets transiting bright stars. We obtain a flat transmission spectrum for HAT-P-26b in the range of 490–900 nm that can be explained by the presence of a grey opacity cloud deck, and indications of transit timing variations, both of which are consistent with previous measurements.

Growth of Bacillus toyonensis in Tofu Wastewater

Bacillus toyonensis has been isolated in Dumai mangrove ecosystem of Riau Province. One of factors affecting the growth of the bacteria is growth substrate. Tofu wastewater is rich in nutrition which can be used as substrate for bacterial growth. This research aimed to observe the growth of B. toyonensis in different concentration of tofu wastewater. The bacteria was grown in tofu wastewater at concentrations 8%, 10% and 12% was supplemented with 0.1 g K2HPO4, 0.15 g KH2PO4, 0.15 g NaCl and 0.5 g vitamin B12 in 100 mL distilled water. The bacterial growth was observed by using spectrophotometer at λ 610 nm and by analysis the total plate counts on plate count agar (PCA) at 0, 24, 48, 72 and 96 hour cultivation. Spectrophotometric observation showed that the highest bacterial growth of all tofu wastewater treatments indicated by the addition of 12% tofu wastewater, although the absorbance value was lower than culture in tryptic soy broth (TSB) as control. Exponential growth occurred between 0-24 hour incubation, and the highest growth indicated in substrate contained 12% tofu wastewater. Similarly, total plate count (TPC) analysis indicated that the highest bacterial growth of all treatment occurred at 24 hours incubation, and the highest count was also indicated by treatment of 12% tofu wastewater (2.42±0.06×108 CFU/mL). In conclusion, tofu wastewater can be an alternative substrate for the bacterial growth.

Internal calibration of Gaia BP/RP low-resolution spectra

Context. The full third Gaia data release will provide, for the first time, the calibrated spectra obtained with the blue and red Gaia slitless spectrophotometers (BP and RP, respectively). Gaia is a very complex mission and cannot be considered as a single instrument, but rather as many instruments. The two lines of sight with wide fields of view introduce strong variations of the observations across the large focal plane with more than one hundred different detectors. The main challenge when facing Gaia spectral calibration is that no lamp spectra or flat fields are available during the mission. Also, the significant size of the line spread function with respect to the dispersion of the prisms produces alien photons contaminating neighbouring positions of the spectra. This makes the calibration special and different from standard approaches. Aims. This work gives a detailed description of the internal calibration model for the spectrophotometric data used to obtain the content of the Gaia catalogue. The main purpose of the internal calibration is to bring all the epoch spectra onto a common flux and pixel (pseudo-wavelength) scale, taking into account variations over the focal plane and with time, producing a mean spectrum from all the observations of the same source. Methods. In order to describe all observations on a common mean flux and pseudo-wavelength scale, we constructed a suitable representation of the internally calibrated mean spectra via basis functions, and we described the transformation between non-calibrated epoch spectra and calibrated mean spectra via a discrete convolution, parametrising the convolution kernel to recover the relevant coefficients. Results. The model proposed here for the internal calibration of the Gaia spectrophotometric observations is able to combine all observations into a mean instrument to allow the comparison of different sources and observations obtained with different instrumental conditions along the mission and the generation of mean spectra from a number of observations of the same source. We derived a calibration model that can handle the self-calibrating nature of the problem. The output of this model provides the internal mean spectra, not as a sampled function (flux and wavelength), but as a linear combination of basis functions, although sampled spectra can easily be derived from them.

Mrk 1239: a Type-2 Counterpart of Narrow-line Seyfert-1?

Abstract We present new spectrophotometric and spectropolarimetric observations of Mrk 1239, one of the 8 prototypes that defines type-1 narrow-line Seyfert galaxies (NLS1s). Unlike the other typical NLS1s though, a high degree of polarization (P ∼ 5.6%) and red optical–IR (g–W 4 = 12.35) colors suggest that Mrk 1239 is more similar to type-2 active galactic nuclei like NGC 1068. Detailed analysis of spectral energy distribution in the UV–optical–IR yields two components from the nucleus: a direct and transmitted component that is heavily obscured (E B–V ≈ 1.6), and another indirect and scattered one with mild extinction (E B–V ∼ 0.5). Such a two-light-paths scenario is also found in previous reports based on the X-ray data. Comparison of emission lines and the detection of He i*λ10830 BAL at [−3000, −1000] km s−1 indicates that the obscuring clouds are at physical scale between the sublimation radius and that of the narrow emission line regions. The potential existence of powerful outflows is found as both the obscurer and scatterer are outflowing. Similar to many other type-2s, jet-like structure in the radio band is found in Mrk 1239, perpendicular to the polarization angle, suggesting polar scattering. We argue that Mrk 1239 is very probably a type-2 counterpart of NLS1s. The identification of 1 out of 8 prototype NLS1s as a type-2 counterpart implies that there can be a substantial amount of analogs of Mrk 1239 misidentified as type-1s in the optical band. Properties of these misidentified objects are going to be explored in our future works.

Operational Diagnosis of Arctic Waters with Instrumental Technology and Information Modeling

As a tool for assessing water quality in the Arctic Basin, a new technology is proposed based on the coupling of spectral observations of multi-channel optical sensors and mathematical model estimates for the qualitative and quantitative distribution of water pollutants. Adaptive spectrophotometer and spectroellipsometer structures are used to carry out the observations, the operation of which is described in detail. The mathematical model used relates to the spatial simulation of the dynamics of pollutants in the Arctic basin and was developed to assess the distribution of pollutants in Arctic aquariums, including Norway and the Bering Sea. In particular, a model is adopted for the study of heavy metals, oil hydrocarbons, phosphates, and other possible water pollutants. This model describes the interactions of pollutants with components of arctic ecosystems, including chlorophyll-a. It is shown that the proposed tool for combining spectrophotometric or spectroellipsometric observation equipment with the developed model provides to a very large extent the reliable distribution of heavy metals and oil hydrocarbons in all Arctic water.

The Coma Dust of Comet C/2013 US10 (Catalina): A Window into Carbon in the Solar System

Abstract Comet C/2013 US10 (Catalina) was a dynamically new Oort cloud comet whose apparition presented a favorable geometry for observations near close-Earth approach (≃0.93 au) at heliocentric distances ≲2 au when insolation and sublimation of volatiles drive maximum activity. Here we present mid-infrared 6.0 ≲ λ(μm) ≲ 40 spectrophotometric observations at two temporal epochs from NASA’s Stratospheric Observatory for Infrared Astronomy and the NASA Infrared Telescope Facility that yield an inventory of the refractory materials and their physical characteristics through thermal modeling analysis. The grain composition is dominated by dark dust grains (modeled as amorphous carbon) with a silicate-to-carbon ratio ≲0.9, little crystalline stoichiometry (no distinct 11.2 μm feature attributed to Mg-rich crystalline olivine), and the submicron grain-size distribution peaking at ≃0.6 μm. The 10 μm silicate feature was weak, ≈12.8% ± 0.1% above the local continuum, and the bolometric grain albedo was low (≲14%). Comet C/2013 US10 (Catalina) is a carbon-rich object. This material, which is well represented by the optical constants of amorphous carbon, is similar to the material that darkens and reddens the surface of comet 67P/Churyumov–Gerasimenko. We argue this material is endemic to the nuclei of comets, synthesizing results from the study of Stardust samples, interplanetary dust particle investigations, and micrometeoritic analyses. The atomic carbon-to-silicate ratio of comet C/2013 US10 (Catalina) and other comets joins a growing body of evidence suggesting the existence of a C/Si gradient in the primitive solar system, providing new insight into planetesimal formation and the distribution of isotopic and compositional gradients extant today.

SN 2017gci: a nearby Type I Superluminous Supernova with a bumpy tail

ABSTRACT We present and discuss the optical spectrophotometric observations of the nearby (z = 0.087) Type I superluminous supernova (SLSN I) SN 2017gci, whose peak K-corrected absolute magnitude reaches Mg = −21.5 mag. Its photometric and spectroscopic evolution includes features of both slow- and of fast-evolving SLSN I, thus favoring a continuum distribution between the two SLSN-I subclasses. In particular, similarly to other SLSNe I, the multiband light curves (LCs) of SN 2017gci show two re-brightenings at about 103 and 142 d after the maximum light. Interestingly, this broadly agrees with a broad emission feature emerging around 6520 Å after ∼51 d from the maximum light, which is followed by a sharp knee in the LC. If we interpret this feature as Hα, this could support the fact that the bumps are the signature of late interactions of the ejecta with a (hydrogen-rich) circumstellar material. Then we fitted magnetar- and CSM-interaction-powered synthetic LCs on to the bolometric one of SN 2017gci. In the magnetar case, the fit suggests a polar magnetic field Bp ≃ 6 × 1014 G, an initial period of the magnetar Pinitial ≃ 2.8 ms, an ejecta mass $M_{\rm ejecta}\simeq 9\, \mathrm{M}_\odot $ and an ejecta opacity $\kappa \simeq 0.08\, \mathrm{cm}^{2}\, \rm{g}^{-1}$. A CSM-interaction scenario would imply a CSM mass $\simeq 5\, \mathrm{M}_\odot $ and an ejecta mass $\simeq 12\, \mathrm{M}_\odot $. Finally, the nebular spectrum of phase + 187 d was modeled, deriving a mass of $\sim 10\, {\rm M}_\odot$ for the ejecta. Our models suggest that either a magnetar or CSM interaction might be the power sources for SN 2017gci and that its progenitor was a massive ($40\, {\rm M}_\odot$) star.

Stellar Spins in the Open Cluster NGC 2516

Abstract Measuring the distribution of stellar spin axis orientations in a coeval group of stars probes the physical processes underlying the stars’ formation. In this paper, we use spectrophotometric observations of the open cluster NGC 2516 to determine the degree of spin alignment among its stars. We combine TESS light curves, ground-based spectroscopy from the Gaia-ESO and GALAH surveys, broadband stellar magnitudes from several surveys, and Gaia astrometry to measure 33 stellar inclinations and quantify overall cluster rotation. Our measurements suggest that stellar spins in this cluster are isotropically oriented, while allowing for the possibility that they are moderately aligned. An isotropic distribution of NGC 2516 spins would imply a star-forming environment in which turbulence dominated ordered motion, while a moderately aligned distribution would suggest a more substantial contribution from rotation. We also perform a three-dimensional analysis of the cluster’s internal kinematics, finding no significant signatures of overall rotation. Stemming from this analysis, we identify evidence of cluster contraction, suggesting possible ongoing mass segregation in NGC 2516.

Benchmarking the fundamental parameters of Ap stars with optical long-baseline interferometric measurements

Context. The variety of physical processes at play in chemically peculiar stars makes it difficult to determine their fundamental parameters. In particular, for the magnetic ones, called Ap stars, the strong magnetic fields and the induced spotted stellar surfaces may lead to biased effective temperatures when these values are derived through spectro-photometry. Aims. We propose to benefit from the exquisite angular resolution provided by long-baseline interferometry in the visible to determine the accurate angular diameters of a number of Ap stars, and thus estimate their radii by a method that is as independent as possible of atmospheric models. Methods. We used the visible spectrograph VEGA at the CHARA interferometric array to complete the sample of Ap stars currently observable with this technique. We estimated the angular diameter and radius of six new targets. We estimated their bolometric flux based solely on observational spectroscopic and photometric data to derive nearly model-independent luminosities and effective temperatures. Results. We extend to 14 the number of Ap stars for which interferometric angular diameters have been measured. The fundamental parameters we derived for the complete Ap sample are compared with those obtained through a self-consistent spectroscopic analysis. Based on a model fitting approach of high-resolution spectra and spectro-photometric observations over a wide wavelength range, this method takes into account the anomalous chemical composition of the atmospheres and the inhomogeneous vertical distribution for different chemical elements. Regarding both the radii and the effective temperatures, the derived values from our interferometric observations and from self-consistent modelling are consistent within better than 2σ for nine targets out of ten. We thus benchmark nine Ap stars for effective temperatures ranging from 7200 and 9100 K, and luminosities ranging between 7 L⊙ and 86 L⊙. Conclusions. These results will be key for the future derivation of accurate radii and other fundamental parameters of fainter peculiar stars for which both the sensitivity and the angular resolution of the current interferometers are not sufficient. Within the context of the observations of Ap stars with the Transiting Exoplanet Survey Satellite (TESS), these interferometric measurements are crucial for testing the mechanism of pulsation excitation at work in these peculiar stars. In particular, our interferometric measurements provide accurate locations in the Hertzsprung-Russell diagram for hot Ap stars among which pulsations may be searched for with TESS, putting to test the blue edge of the theoretical instability strip. These accurate locations could be used to derive masses and ages of these stars through a specific grid of models, and to test correlations between the properties of these peculiar stars and their evolutionary state.