Photometric Observations Research Articles

Detection of Eclipses in the Cataclysmic Variable LAMOST J035913.61 + 405035.0

ABSTRACTI conducted photometric observations of the cataclysmic variable LAMOST J035913.61 + 405035.0 and detected eclipses. During these observations, I recorded 14 eclipses over two groups of nights separated by 13 months. I accurately determined the orbital period of the system to be days. For the eclipses, I derived an ephemeris which is valid for a long time and suitable for studying changes in the orbital period. The out‐of‐eclipse magnitude of the star varied between 15.32 ± 0.02 and 17.25 ± 0.08 mag. As the brightness decreased, the eclipses became deeper and narrower. The average depth of eclipses was 1.35 ± 0.10 mag, and the average width at half‐depth was 16.9 ± 0.7 min. I estimated the range of possible orbital inclinations to be between 72.8° and 76.0°, and the range of average absolute V‐band magnitudes of the disc to be between 5.16 ± 0.15 and 5.44 ± 0.15 mag. Although based on the light curve from the ZTF survey, LAMOST J035913.61 + 405035.0 showed only small outbursts with amplitudes below 1.5 mag, it should be classified as a dwarf nova because the average disc brightness and mass transfer rate were below the limit of thermal instability.

Long-period double-lined eclipsing binaries: the system V454 Aur with the secondary eclipse caused by the occultation of the hotter component

Abstract We present the results of our study of the long-period eclipsing binary star \Aur. The results are based on spectroscopic data obtained with the UFES \'echelle spectrograph and photometric observations from TESS. The derived radial velocity curve is based on 17 spectra obtained between 2021 and 2023, covering all orbital phases of this binary system. The orbital period determined from TESS data, $P = 27.019803 \pm 0.000003$ days, agrees within uncertainties with the period established in previous studies. The model constructed for the TESS photometric light curve achieves a precision of 0.01\%. The effective temperatures of both components, as well as the system metallicity, were directly derived from the spectra and are $T_\mathrm{eff, A} = 6250 \pm 50$\,K, $T_\mathrm{eff, B} = 5855 \pm 50$\,K, and $\mathrm{[Fe/H]} = -0.10 \pm 0.08$, respectively. Our analysis of the photometric and spectroscopic data allowed us to directly compute the luminosities of the components, $L_A = 1.82\,L_\odot$ and $L_B = 1.07\,L_\odot$, their radii, $R_A = 1.15\,R_\odot$ and $R_B = 1.00\,R_\odot$, and their masses, $M_A = 1.137\,M_\odot$ and $M_B = 1.023\,M_\odot$, with uncertainties below 1\%. Comparison with evolutionary tracks indicates that the system's age is $1.18 \pm 0.10$\,Gyr, and both components are still on the main sequence. The \Aur\ system is particularly interesting due to the partial eclipse of the primary component, which results in the ``inversion'' of the primary and secondary minima in the photometric light curve.

PAStar: A model for stellar surface from the Sun to active stars

Context. The characterisation of exoplanets requires a good description of the host star. Stellar activity acts as a source of noise, which can alter planet radii as derived from the transit depth or atmospheric characterisation. Aims. Here, we propose PAStar, a model to describe photospheric activity in the form of spots and faculae, which could be applied to a wide range of stellar observations, from photometric to spectroscopic time series, making it possible to correctly extract planetary and stellar properties. Methods. The adopted stellar atmosphere is a combination of three components: the quiet photosphere, spots, and faculae. The model takes into account the effects of star inclination and Doppler shifts due to stellar rotation and limb darkening, which is independent for each component. Several synthetic products have been presented to show the capabilities of the model. Results. The model is able to retrieve the input surface-inhomogeneity configuration through photometric or spectroscopic observations. The model has been validated against optical solar data and compared to alternative stellar surface activity models; for example SOAP code. The Sun is a unique laboratory to test stellar models because of the possibility to unambiguously relate flux variations to surface inhomogeneities’ configuration. This validation has been done by analysing a photometric time series from the Variability of Solar Irradiance and Gravity Oscillations (VIRGO) photometer on-board Solar and Heliospheric Observatory (SOHO) mission. Results have been compared to real solar images from the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) to confirm the goodness of the results in terms of surface inhomogeneities’ positions and dimensions. Conclusions. The description of stellar activity is a fundamental step in several astrophysical contexts and it is covered by the method we present. Our model offers a flexible and valuable tool to describe the activity of stars when it is dominated by spots and faculae.

O’Connell Effect and Period Variations on Solar-like Contact Binary EF Boo

Abstract Using ground-based telescopes, the multi-color photometric observations of the contact binary EF Boo were obtained in 2020, 2023, and 2024. Combining these with 7-sectors of light curves from TESS data, the variations of O’Connell effect in continuous time and shapes of light curve over several years were identified. Three sets of the typical light curves were analyzed to determine the photometric solutions via Wilson-Devinney program. Considering the spectroscopic mass ratio of q = 0.53, these photometric solutions suggest that EF Boo is a W-type W UMa contact binary with a filling factor of f=22.26%, a small temperature difference, and a cool spot on the primary component. If the variations of the O’Connell effect is due to magnetic activity of this cool spot, the longitudinal location varied from 50.4° to 302.7° over the time interval of 1434 days. Based on all CCD minimum times from ground-based telescope and TESS data, the O-C curve was also analyzed. A cyclic oscillation (A3=0.00575 days, T3=27.8 years) superimposed on a secular decrease (dP/dt=6.74×10-8 day year-1) was found for the first time. The successive increase is possibly as a result of mass transfer from the less massive component to the more massive one. The cyclic oscillations were possibly explained by the light-travel time effect via a third body, or the magnetic activities. From the short cadence observations from TESS, we calculated the value of the O'Connell effect and O-C value for each cycle, and found no correlation between the O'Connell effect with O-C in nearly 30 days across different sectors.

Transit-timing variations in the AU Mic system observed with CHEOPS

AU Mic is a very active M dwarf star with an edge-on debris disk and two known transiting sub-Neptunes with a possible third planetary companion. The two transiting planets exhibit significant transit-timing variations (TTVs) that are caused by the gravitational interaction between the bodies in the system. Using photometrical observations taken with the CHaracterizing ExOPlanet Satellite (CHEOPS), we aim to constrain the planetary radii, the orbital distances, and the periods of AU Mic b and c. Furthermore, our goal is to determine the superperiod of the TTVs for AU Mic b and to update the transit ephemeris for both planets. Additionally, based on the perceived TTVs, we study the possible presence of a third planet in the system. We conducted ultra-high precision photometric observations with CHEOPS in 2022 and 2023. We used Allesfitter to fit the planetary transits and to constrain the planetary and orbital parameters. We combined our new measurements with results from previous years to determine the periods and amplitudes of the TTVs. We applied dynamical modelling based on TTV measurements from the 2018-2023 period to reconstruct the perceived variations. We found that the orbital distances and periods for AU Mic b and c agree with the results from previous works. However, the values for the planetary radii deviate slightly from previous values, which we attribute to the effect of spots on the stellar surface. AU Mic c showed very strong TTVs, with transits that occurred ∼80 minutes later in 2023 than in 2021. Through a dynamical analysis of the system, we found that the observed TTVs can be explained by a third planet with an orbital period of ∼12.6 days and a mass of 0.203^ M_⊕. We explored the orbital geometry of the system and found that AU Mic c has a misaligned retrograde orbit. The limited number of AU Mic observations prevented us from determining the exact dynamical configuration and planetary parameters. Further monitoring of the system with CHEOPS might help to improve these results.

Debris disks around M dwarfs: The Herschel DEBRIS survey

The Herschel open-time key program Disc Emission via a Bias-free Reconnaissance in the Infrared and Sub-millimeter (DEBRIS) is an unbiased survey of the nearest ∼ 100 stars for each stellar type A-M observed with a uniform photometric sensitivity to search for cold debris disks around them. The analysis of the Photoconductor Array Camera and Spectrometer (PACS) photometric observations of the 94 DEBRIS M dwarfs of this program is presented in this paper, following upon two companion papers on the DEBRIS A-star and FGK-star subsamples. In the M-dwarf subsample, two debris disks have been detected, around the M3V dwarf GJ 581 and the M4V dwarf Fomalhaut C (LP 876-10). This result gives a disk detection rate of $2.1^ $ % at the 68% confidence level, significantly less than measured for earlier stellar types in the DEBRIS program. However, we show that the survey of the DEBRIS M-dwarf subsample is about ten times shallower than the surveys of the DEBRIS FGK subsamples when studied in the physical parameter space of the disk's fractional dust luminosity versus blackbody radius. Furthermore, had the DEBRIS K-star subsample been observed at the same shallower depth in this parameter space, its measured disk detection rate would have been statistically consistent with the one found for the M-dwarf subsample. Hence, the incidence of debris disks does not appear to drop from the K subsample to the M subsample of the DEBRIS program, when considering disks in the same region of physical parameter space. An alternative explanation is that the only two bright disks discovered in the M-dwarf subsample would not, in fact, be statistically representative of the whole population.

Eruptive mass loss less than a year before the explosion of superluminous supernovae. I. The cases of SN,2020xga and SN,2022xgc

We present photometric and spectroscopic observations of and two hydrogen-poor superluminous supernovae (SLSNe-I) at z = 0.4296 and z = 0.3103, respectively, which show an additional set of broad Mg II absorption lines, blueshifted by a few thousands kilometer second^-1 with respect to the host galaxy absorption system. Previous work interpreted this as due to resonance line scattering of the SLSN continuum by rapidly expanding circumstellar material (CSM) expelled shortly before the explosion. The peak rest-frame g-band magnitude of is -22.30 ± 0.04 mag and of is -21.97 ± 0.05 mag, placing them among the brightest SLSNe-I. We used high-quality spectra from ultraviolet to near-infrared wavelengths to model the Mg II line profiles and infer the properties of the CSM shells. We find that the CSM shell of resides at ∼ 1.3 cm, moving with a maximum velocity of $4275 km $, and the shell of is located at ∼ 0.8 cm, reaching up to $4400 km $. These shells were expelled ∼ 11 and ∼ 5 months before the explosions of and respectively, possibly as a result of luminous-blue-variable-like eruptions or pulsational pair instability (PPI) mass loss. We also analyzed optical photometric data and modeled the light curves, considering powering from the magnetar spin-down mechanism. The results support very energetic magnetars, approaching the mass-shedding limit, powering these SNe with ejecta masses of ∼ 7-9 M_⊙. The ejecta masses inferred from the magnetar modeling are not consistent with the PPI scenario pointing toward stars $> 50 M_⊙$ He-core; hence, alternative scenarios such as fallback accretion and CSM interaction are discussed. Modeling the spectral energy distribution of the host galaxy of reveals a host mass of 10^7.8 rm M_⊙, a star formation rate of $ rm M_⊙ yr^-1, and a metallicity of ∼ 0.2 rm Z_⊙.

The changing-look AGN SDSS J101152.98+544206.4 is returning to a type I state

Aims. We discovered that the changing-look active galactic nucleus (CLAGN) SDSS J101152.98+544206.4 (J1011+5442 for short) gradually returns to the type I state after a short period between 2014 and 2019 in the faint type 1.9 state. Methods. Motivated by the rebrightening in the optical and mid-infrared light curves from ZTF and WISE, we obtained new spectroscopic observations with the Xinglong 2.16 m, the Lijiang 2.4 m, and the MMT 6.5 m optical telescopes in 2024. Results. After changing its optical AGN type from 1 to 1.9 between 2003 and 2015 according to the repeat spectroscopy from the Time Domain Spectroscopic Survey, J1011+5442 returned to its type I state in 2024. We detect the significant and very broad Hβ lines (full width at half maximum of ≳5000 km/s) based on the new spectra, which suggests that J1011+5442 was in the intermediate state between the dim state in 2015 and the bright state in 2003. The long-term optical and mid-infrared light curves also show a brightening trend between 2019 and 2024 as the broad Hβ line appeared. The time lag of about 100 days between the mid-infrared and optical variability is consistent with the prediction of dust reverberation mapping. Conclusions. The behavior of the photometric and spectroscopic observations of J1011+5442 is consistent with the argument that the repeating changing-look phenomenon is regulated by the variation in the accretion rate.

High-time-cadence Spectroscopy and Photometry of Stellar Flares on M dwarf YZ Canis Minoris with the Seimei Telescope and TESS. I. Discovery of Rapid and Short-duration Prominence Eruptions

M dwarfs show frequent flares and associated coronal mass ejections (CMEs) may significantly impact close-in habitable planets. M dwarf flares sometimes show blue/red asymmetries in the Hα line profile, suggesting prominence eruptions as an early stage of CMEs. However, their high-time-cadence observations are limited. We conducted spectroscopic monitoring observations of the active M dwarf YZ Canis Minoris with an ∼1 minute time cadence using the Seimei telescope, simultaneously with the optical photometric observations by Transiting Exoplanet Survey Satellite. We detected 27 Hα flares with Hα energies ranging from 1.7 × 1029 to 3.8 × 1032 erg and durations from 8 to 319 minutes. Among them, we identified three blue asymmetry and five red asymmetry events based on criteria using the Bayesian information criterion. The maximum velocity of the blueshifted and redshifted components ranges from 200 to 450 km s−1 and 190 to 400 km s−1, respectively. The duration and time evolution show variety, and in particular, we discovered rapid, short-duration blue/red asymmetry events with the duration of 6–8 minutes. Among the eight blue/red asymmetry events, two blue and one red asymmetry events are interpreted as prominence eruptions because of their fast velocity and time evolution. Based on this interpretation, the lower limit of occurrence frequency of prominence eruptions can be estimated to be ∼1.1 events per day. Our discovery of short-duration events suggests that previous studies with low time cadence may have missed these events, potentially leading to an underestimation of the occurrence frequency of prominence eruptions/CMEs.

ET Dra activity according to observations in 2018–2023

The results of new photometric observations of the chromospherically active star ET Dra, performed using telescopes of the Zvenigorod INASAN Observatory, the Russian-Cuban Observatory in the territory of the Republic of Cuba (Havana) and the Terskol INASAN Observatory (a total of 8 sets of observations), as well as the addition of archival observations of the Kamogata Wide-field Survey. According to the data received during 2018–2023 changes in the shape of the light curve caused by the rotational modulation of a star with spots on the surface, as well as studies of the long-term variability of the star’s brightness were investigated. Characteristic changes in the ET Dra light curve are noted including a decrease of the stellar brightness in V filter, its cyclic changes and subsequent brightness increase. The shape of the phase curve and the duration of the extended minimum of brightness vary. During the HJD 245 9670 – 245 9715 interval the amplitude of the star’s brightness variability reached a maximum value of more than 0.4 magnitude, as it was in 1990. For each of the 8 set of observations the surface temperature inhomogeneities map were calculated and estimates of the spotedness parameter S of the object were performed. Maximum value of parameter S was 32.2–33.5%. Based on the constructed power spectra the values of possible cycles of long-term activity of the star are obtained as 570 and 1160 days (1.56 and 3.18 years).

Determination of dynamic and physical characteristics of near-Earth asteroids based on observations from 2022–2023

Astrometric and multicolor photometric observations of near-Earth asteroids have been made at the SBG telescopes of the Kourovka Astronomical Observatory of the UrFU and the Zeiss-1000 telescope of the Simeiz Observatory in 2022–2023. Improved orbital elements were obtained for seven asteroids from astrometric observations at the SBG telescope. Axial rotation periods were estimated from photometric observations for seven asteroids. Color indices for six asteroids were obtained from photometric observations in B, V, R, and I filters.

Determining the structure of the atmosphere exoplanet HD 189733 b based on multicolor photometric transit observations

The work carried out an analysis and interpretation of light curves obtained with observing with the HST telescope the transit of the exoplanet HD 189733 b across the disk of the star. Observations were carried out in a wide range of wavelengths 5500–10500 Å, which made it possible to identify the relationship between the wavelength and the data obtained during the interpretation of the radius of the planet. It has also been shown that this dependence can be explained by the presence of a Rayleigh atmosphere on the planet, and an approximate assessment of the possible parameters of this atmosphere was also carried out.

Stellar atmospheric parameters and chemical abundances of ~ 5 million stars from S-PLUS multiband photometry

The APOGEE, GALAH, and LAMOST spectroscopic surveys have substantially contributed to our understanding of the Milky Way by providing a wide range of stellar parameters and chemical abundances. Complementing these efforts, photometric surveys that include narrowband and medium-band filters, such as Southern Photometric Local Universe Survey (S-PLUS), provide a unique opportunity to estimate the atmospheric parameters and elemental abundances for a much larger number of sources, compared to spectroscopic surveys. Our aim is to establish methodologies for extracting stellar atmospheric parameters and selected chemical abundances from S-PLUS photometric data, which cover approximately $3000$ square degrees, by applying seven narrowband and five broadband filters. We used all 66 S-PLUS colors to estimate parameters based on three different training samples from the LAMOST, APOGEE, and GALAH surveys, applying cost-sensitive neural network (NN) and random forest (RF) algorithms. We kept the stellar abundances that lacked corresponding absorption features in the S-PLUS filters to test for spurious correlations in our method. Furthermore, we evaluated the effectiveness of the NN and RF algorithms by using estimated $T_ eff $ and \( g\) values as the input features to determine other stellar parameters and abundances. The NN approach consistently outperforms the RF technique on all parameters tested. Moreover, incorporating $T_ eff $ and \( g\) leads to an improvement in the estimation accuracy by approximately $3<!PCT!>$. We kept only parameters with a goodness-of-fit higher than $50<!PCT!>$. Our methodology allowed us to obtain reliable estimates for fundamental stellar parameters ($T_ eff g\), and Fe/H ) and elemental abundance ratios such as alpha /Fe Al/Fe C/Fe Li/Fe and Mg/Fe for approximately five million stars across the Milky Way, with a goodness-of-fit above $60<!PCT!>$. We also obtained additional abundance ratios, including Cu/Fe O/Fe and Si/Fe . However, these ratios should be used cautiously due to their low accuracy or lack of a clear relationship with the S-PLUS filters. Validation of our estimations and methods was performed using star clusters, Transiting Exoplanet Survey Satellite (TESS) data and Javalambre Photometric Local Universe Survey (J-PLUS) photometry, further demonstrating the robustness and accuracy of our approach. By leveraging S-PLUS photometric data and advanced machine learning techniques, we have established a robust framework for extracting fundamental stellar parameters and chemical abundances from medium-band and narrowband photometric observations. This approach offers a cost-effective alternative to high-resolution spectroscopy. The estimated parameters hold significant potential for future studies, particularly when classifying objects within our Milky Way or gaining insights into its various stellar populations.

Spectroscopic observations of flares and superflares on AU Mic

ABSTRACT The young active flare star AU Mic is the planet host star with the highest flare rate from Transiting Exoplanet Survey Satellite data. Therefore, it represents an ideal target for dedicated ground-based monitoring campaigns with the aim to characterize its numerous flares spectroscopically. We performed such spectroscopic monitoring with the ESO1.52-m telescope of the PLATOSpec consortium. In more than 190 h of observations, we find 24 flares suitable for detailed analysis. We compute their parameters (duration, peak flux, and energy) in eight chromospheric lines (H $\alpha$, H $\beta$, H $\gamma$, H $\delta$, Na i D1&D2, He i D3, He i 6678) and investigate their relationships. Furthermore, we obtained simultaneous photometric observations and low-resolution spectroscopy for part of the spectroscopic runs. We detect one flare in the g$^{\prime }$-band photometry, which is associated with a spectroscopic flare. Additionally, an extreme flare event occurred on 2023-09-16 of which only a time around its possible peak was observed, during which chromospheric line fluxes were raised by up to a factor of three compared to the following night. The estimated energy of this event is around $10^{33}$ erg in H $\alpha$ alone, i.e. a rare chromospheric line superflare.

Flare from the secondary star of an extreme period binary

Abstract Photometric observations were conducted on the short-period and highly active M dwarf BX Tri from 2016 to 2023. From ground-based observations and data from the Transiting Exoplanet Survey Satellite (TESS), a total of 196 sets of light curves were analyzed using Wilson–Devinney (W-D) method. The photometric analyses of BX Tri reveal a semidetached configuration, where the primary star accounts for a minimum of $80\%$ of the total luminosity in this binary system. The magnetic activity cycle of BX Tri was determined to be $9.4\:$yr, as indicated by the variability in spot longitudes. Three flares were detected by TESS. The long-lasting flare$_{1797}$ could originate from a polar region on the secondary star. Given the ongoing flare eruptions, BX Tri has the potential to merge into a single star through mergebursts.

CSS 161010: A Luminous Fast Blue Optical Transient with Broad Blueshifted Hydrogen Lines

We present ultraviolet, optical, and near-infrared photometric and optical spectroscopic observations of the luminous fast blue optical transient (LFBOT) CSS 161010:045834–081803 (CSS 161010). The transient was found in a low-redshift (z = 0.033) dwarf galaxy. The light curves of CSS 161010 are characterized by an extremely fast evolution and blue colors. The V-band light curve shows that CSS 161010 reaches an absolute peak of MVmax=−20.66±0.06 mag in 3.8 days from the start of the outburst. After maximum, CSS 161010 follows a power-law decline ∝t −2.8±0.1 in all optical bands. These photometric properties are comparable to those of well-observed LFBOTs such as AT 2018cow, AT 2020mrf, and AT 2020xnd. However, unlike these objects, the spectra of CSS 161010 show a remarkable transformation from a blue and featureless continuum to spectra dominated by very broad, entirely blueshifted hydrogen emission lines with velocities of up to 10% of the speed of light. The persistent blueshifted emission and the lack of any emission at the rest wavelength of CSS 161010 are unique features not seen in any transient before CSS 161010. The combined observational properties of CSS 161010 and its M * ∼ 108 M ⊙ dwarf galaxy host favor the tidal disruption of a star by an intermediate-mass black hole as its origin.

SN2023fyq: A Type Ibn Supernova with Long-standing Precursor Activity Due to Binary Interaction

We present photometric and spectroscopic observations of SN 2023fyq, a Type Ibn supernova (SN) in the nearby galaxy NGC 4388 (D ≃ 18 Mpc). In addition, we trace the 3 yr long precursor emission at the position of SN 2023fyq using data from DLT40, ATLAS, Zwicky Transient Facility, ASAS-SN, Swift, and amateur astronomer Koichi Itagaki. The double-peaked postexplosion light curve reaches a luminosity of ∼1043 erg s−1. The strong intermediate-width He lines observed in the nebular spectrum imply the interaction is still active at late phases. We found that the precursor activity in SN 2023fyq is best explained by the mass transfer in a binary system involving a low-mass He star and a compact companion. An equatorial disk is likely formed in this process (∼0.6M ⊙), and the interaction of SN ejecta with this disk powers the second peak of the SN. The early SN light curve reveals the presence of dense extended material (∼0.3M ⊙) at ∼3000R ⊙ ejected weeks before the SN explosion, likely due to final-stage core silicon burning or runaway mass transfer resulting from binary orbital shrinking, leading to rapid-rising precursor emission within ∼30 days prior to explosion. The final explosion could be triggered either by the core collapse of the He star or by the merger of the He star with a compact object. SN 2023fyq, along with SN 2018gjx and SN 2015G, forms a unique class of Type Ibn SNe, which originate in binary systems and are likely to exhibit detectable long-lasting pre-explosion outbursts with magnitudes ranging from −10 to −13.

Maven: a multimodal foundation model for supernova science

Abstract A common setting in astronomy is the availability of a small number of high-quality observations, and larger amounts of either lower-quality observations or synthetic data from simplified models. Time-domain astrophysics is a canonical example of this imbalance, with the number of supernovae observed photometrically outpacing the number observed spectroscopically by multiple orders of magnitude. At the same time, no data-driven models exist to understand these photometric and spectroscopic observables in a common context. Contrastive learning objectives, which have grown in popularity for aligning distinct data modalities in a shared embedding space, provide a potential solution to extract information from these modalities. We present Maven, the first foundation model for supernova science. To construct Maven, we first pre-train our model to align photometry and spectroscopy from 0.5 M synthetic supernovae using a contrastive objective. We then fine-tune the model on 4702 observed supernovae from the Zwicky transient facility. Maven reaches state-of-the-art performance on both classification and redshift estimation, despite the embeddings not being explicitly optimized for these tasks. Through ablation studies, we show that pre-training with synthetic data improves overall performance. In the upcoming era of the Vera C. Rubin observatory, Maven will serve as a valuable tool for leveraging large, unlabeled and multimodal time-domain datasets.

Tropopause Height Inferred from Twilight Photometry

Abstract The tropopause height has been measured by sounding balloons for more than 70 years. More recently, lidar has found the tropopause height by detecting aerosols or subvisible cirrus that accumulates at the tropopause. Here, we present a twilight photometer technique to detect the tropopause height with results close to the traditional World Meteorological Organization (WMO) method from sounding balloon measurements. The twilight intensity I, although radiometrically uncalibrated, can be normalized by the derivative of log(I) with respect to time t, or I′(t)/(t), to infer stratospheric aerosol layer properties using Earth’s shadow to orderly shield the sunlight below different altitudes. A conventional twilight photometer detects the twilight glow from atmospheric aerosol scattering with a photodiode detector equipped with a near-infrared optical filter. We have replaced the photodiode and optical filter with a light-emitting diode (LED) that functions as a wavelength-dependent photodiode with a narrowband response near 1050 nm. We found that the layer height from twilight photometer observations is highly correlated with the tropopause height. Seventy-six twilight tropopause heights during the first 6 months of 2024 at Geronimo Creek Atmospheric Monitoring Station (GCAMS) in Central Texas agree well with those reported by sounding balloons launched from Corpus Christi, Texas, 207 km from GCAMS (standard deviation of 265 m). The twilight method is inexpensive, easily implemented, and has potential for use at remote sites with solar power and developing countries that lack resources for sounding balloons. It can also provide a learning tool for students of meteorology and the atmospheric sciences.

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.