Multi-band Photometry Research Articles

Central concentration of asymmetric features in post-starburst galaxies at z ∼ 0.8

ABSTRACT We present morphological analyses of post-starburst galaxies (PSBs) at 0.7 < z < 0.9 in the COSMOS field. We fitted ultraviolet to mid-infrared multiband photometry of objects with i < 24 from COSMOS2020 catalogue with population synthesis models assuming non-parametric, piece-wise constant function of star formation history, and selected 94 of those galaxies that have high specific star formation rates (SSFRs) of more than 10−9.5 yr−1 in 321–1000 Myr before observation and an order-of-magnitude lower SSFRs within recent 321 Myr. We devised a new non-parametric morphological index which quantifies concentration of asymmetric features, CA, and measured it as well as concentration C and asymmetry A on the Hubble Space Telescope/Advanced Camera for Surveys IF814W-band images. While relatively high C and low A values of PSBs are similar to those of quiescent galaxies rather than star-forming galaxies, we found that PSBs show systematically higher values of CA than both quiescent and star-forming galaxies; 36 per cent of PSBs have log CA > 0.8, while only 16 per cent (2 per cent) of quiescent (star-forming) galaxies show such high CA values. Those PSBs with high CA have relatively low overall asymmetry of A ∼ 0.1, but show remarkable asymmetric features near the centre. The fraction of those PSBs with high CA increases with increasing SSFR in 321–1000 Myr before observation rather than residual ongoing star formation. These results and their high surface stellar mass densities suggest that those galaxies experienced a nuclear starburst in the recent past, and processes that cause such starbursts could lead to the quenching of star formation through rapid gas consumption, supernova/active galactic nucleus feedback, and so on.

Volume-limited sample of low-mass red giant stars, the progenitors of hot subdwarf stars

Context. Current theory predicts that hot subdwarf binaries are produced from evolved low-mass binaries that have undergone mass transfer and drastic mass loss during either a common-envelope phase or a stable Roche-lobe overflow while on the red giant branch (RGB). Aims. We perform a spectroscopic survey to find binary systems that include low-mass red giants near the tip of the RGB, which are predicted to be the direct progenitors of subdwarf B (sdB) stars. We aim to obtain a homogeneous sample to search for the observational evidence of correlations between the key parameters governing the formation of sdB stars and constrain the physics of stable mass transfer. Methods. Based on data from the Gaia mission and several ground-based, multiband photometry surveys, we compiled a sample of low-mass red giant branch (RGB) candidates. The candidates were selected according to their Gaia data release 2 (DR2) color, absolute magnitude, and proper motion cuts. In this work, we concentrated on the southern hemisphere targets and conducted a spectroscopic survey of 88 red giant stars to search for the long-period RGB plus main-sequence binary systems within 200 pc. Combining radial velocity (RV) measurements from ground-based observations with CORALIE and RV measurements from Gaia DR2 and from the early data release 3 (eDR3) as well as the astrometric excess noise and renormalized unit weight error measurements from Gaia DR3, we defined a robust binary classification method. In addition, we searched for known binary systems in the literature and in Gaia DR3. Results. We select a total of 211 RGB candidates in the southern hemisphere within 200 pc based on the Gaia DR2 color-magnitude diagram. Among them, a total of 33 red giants were reported as binary systems with orbital periods between 100 and 900 days, some of which are expected to be the direct progenitors of wide binary sdB stars. In addition, we classified 37 new main-sequence plus RGB binary candidates, whose orbital parameters will be measured with future spectroscopic follow-up. Conclusions. Using high-quality astrometric measurements provided by the Gaia mission coupled with high-resolution spectroscopy from the ground, we provide a powerful method for searching for low-mass red giant stars in long-period binary systems.

First detection of the outer edge of an AGN accretion disc: very fast multiband optical variability of NGC 4395 with GTC/HiPERCAM and LT/IO:O

ABSTRACT We present fast (∼200 s sampling) $\it ugriz$ photometry of the low -mass AGN NGC 4395 with the Liverpool Telescope, followed by very fast (3 s sampling) us, gs, rs, is, and zs simultaneous monitoring with HiPERCAM on the 10.4m GTC. These observations provide the fastest ever AGN multiband photometry and very precise lag measurements. Unlike in all other AGN, gs lags us by a large amount, consistent with disc reprocessing but not with reprocessing in the broad-line region (BLR). There is very little increase in lag with wavelength at long wavelengths, indicating an outer edge (Rout) to the reprocessor. We have compared truncated disc reprocessing models to the combined HiPERCAM and previous X-ray/UV lags. For the normally accepted mass of 3.6 × 105M⊙, we obtain reasonable agreement with zero spin, Rout ∼ 1700Rg and the done physically motivated temperature-dependent disc colour-correction factor (f$\rm _{col}$). A smaller mass of 4 × 104M⊙ can only be accommodated if f$\rm _{col}=2.4$, which is probably unrealistically high. Disc self gravity is probably unimportant in this low-mass AGN but an obscuring wind may provide an edge. For the small mass, the dust sublimation radius is similar to Rout so the wind could be dusty. However, for the more likely large mass, the sublimation radius is further out so the optically thick base of a line-driven gaseous wind is more likely. The inner edge of the BLR is close to Rout in both cases. These observations provide the first good evidence for a truncated AGN disc and caution that truncation should be included in reverberation lag modelling.

S-PLUS DR1 galaxy clusters and groups catalogue using PzWav

ABSTRACT We present a catalogue of 4499 groups and clusters of galaxies from the first data release of the multi-filter (5 broad, 7 narrow) Southern Photometric Local Universe Survey (S-PLUS). These groups and clusters are distributed over 273 deg2 in the Stripe 82 region. They are found using the PzWav algorithm, which identifies peaks in galaxy density maps that have been smoothed by a cluster scale difference-of-Gaussians kernel to isolate clusters and groups. Using a simulation-based mock catalogue, we estimate the purity and completeness of cluster detections: at S/N > 3.3, we define a catalogue that is 80 per cent pure and complete in the redshift range 0.1 < z < 0.4, for clusters with M200 > 1014 M⊙. We also assessed the accuracy of the catalogue in terms of central positions and redshifts, finding scatter of σR = 12 kpc and σz = 8.8 × 10−3, respectively. Moreover, less than 1 per cent of the sample suffers from fragmentation or overmerging. The S-PLUS cluster catalogue recovers ∼80 per cent of all known X-ray and Sunyaev-Zel’dovich selected clusters in this field. This fraction is very close to the estimated completeness, thus validating the mock data analysis and paving an efficient way to find new groups and clusters of galaxies using data from the ongoing S-PLUS project. When complete, S-PLUS will have surveyed 9300 deg2 of the sky, representing the widest uninterrupted areas with narrow-through-broad multi-band photometry for cluster follow-up studies.

The Panchromatic Hubble Andromeda Treasury: Triangulum Extended Region (PHATTER). IV. Star Cluster Catalog

We construct a catalog of star clusters from Hubble Space Telescope images of the inner disk of the Triangulum Galaxy (M33) using image classifications collected by the Local Group Cluster Search, a citizen science project hosted on the Zooniverse platform. We identify 1214 star clusters within the Hubble Space Telescope imaging footprint of the Panchromatic Hubble Andromeda Treasury: Triangulum Extended Region (PHATTER) survey. Comparing this catalog to existing compilations in the literature, 68% of the clusters are newly identified. The final catalog includes multiband aperture photometry and fits for cluster properties via integrated light spectral energy distribution fitting. The cluster catalog’s 50% completeness limit is ∼1500 M ☉ at an age of 100 Myr, as derived from comprehensive synthetic cluster tests.

Galaxy morphoto-Z with neural Networks (GaZNets)

Aims.In the era of large sky surveys, photometric redshifts (photo-z) represent crucial information for galaxy evolution and cosmology studies. In this work, we propose a new machine learning (ML) tool called Galaxy morphoto-Z with neural Networks (GaZNet-1), which uses both images and multi-band photometry measurements to predict galaxy redshifts, with accuracy, precision and outlier fraction superior to standard methods based on photometry only.Methods.As a first application of this tool, we estimate photo-zfor a sample of galaxies in the Kilo-Degree Survey (KiDS). GaZNet-1 is trained and tested on ∼140 000 galaxies collected from KiDS Data Release 4 (DR4), for which spectroscopic redshifts are available from different surveys. This sample is dominated by bright (MAG_AUTO < 21) and low-redshift (z < 0.8) systems; however, we could use ∼6500 galaxies in the range 0.8 < z < 3 to effectively extend the training to higher redshift. The inputs are ther-band galaxy images plus the nine-band magnitudes and colors from the combined catalogs of optical photometry from KiDS and near-infrared photometry from the VISTA Kilo-degree Infrared survey.Results.By combining the images and catalogs, GaZNet-1 can achieve extremely high precision in normalized median absolute deviation (NMAD = 0.014 for lower redshift and NMAD = 0.041 for higher redshift galaxies) and a low fraction of outliers (0.4% for lower and 1.27% for higher redshift galaxies). Compared to ML codes using only photometry as input, GaZNet-1 also shows a ∼10%−35% improvement in precision at different redshifts and a ∼45% reduction in the fraction of outliers. We finally discuss the finding that, by correctly separating galaxies from stars and active galactic nuclei, the overall photo-zoutlier fraction of galaxies can be cut down to 0.3%.

PROBES. I. A Compendium of Deep Rotation Curves and Matched Multiband Photometry

We present the Photometry and Rotation Curve Observations from Extragalactic Surveys (PROBES) compendium of extended rotation curves for 3163 late-type spirals, with matching homogeneous multiband photometry for 1677 of them. PROBES rotation curves originally extracted from Hα long-slit spectra and aperture synthesis H i (21cm) velocity maps typically extend out to a median 2 R e (or 1 R 23.5,r ). Our uniform photometry takes advantage of GALEX, DESI-LIS, and WISE images and the software AutoProf to yield multiband azimuthally averaged surface brightness profiles that achieve depths greater than 25 mag arcsec−2 (FUV, NUV), 27 mag arcsec−2 (g, r), and 26 mag arcsec−2 (z, W1, and W2). With its library of spatially resolved profiles and an extensive table of structural parameters, the versatile PROBES data set will benefit studies of galaxy structure and formation.

Mira variables in the Milky Way’s nuclear stellar disc: discovery and classification

ABSTRACT The properties of the Milky Way’s nuclear stellar disc give crucial information on the epoch of bar formation. Mira variables are promising bright candidates to study the nuclear stellar disc, and through their period–age relation dissect its star formation history. We report on a sample of 1782 Mira variable candidates across the central $3\times 3\, \mathrm{deg}^2$ of the Galaxy using the multi-epoch infrared VISTA Variables in Via Lactea (VVV) survey. We describe the algorithms employed to select candidate variable stars and then model their light curves using periodogram and Gaussian process methods. By combining with WISE, 2MASS, and other archival photometry, we model the multiband light curves to refine the periods and inspect the amplitude variation between different photometric bands. The infrared brightness of the Mira variables means many are too bright and missed by VVV. However, our sample follows a well-defined selection function as expected from artificial star tests. The multiband photometry is modelled using stellar models with circumstellar dust that characterize the mass-loss rates. We demonstrate how ≳90 per cent of our sample is consistent with O-rich chemistry. Comparison to period–luminosity relations demonstrates that the bulk of the short period stars are situated at the Galactic Centre distance. Many of the longer period variables are very dusty, falling significantly under the O-rich Magellanic Cloud and solar neighbourhood period–luminosity relations and exhibit high mass-loss rates of $\sim 2.5\times 10^{-5}M_\odot \, \mathrm{yr}^{-1}$. The period distribution appears consistent with the nuclear stellar disc forming $\gtrsim 8\, \mathrm{Gyr}$ ago, although it is not possible to disentangle the relative contributions of the nuclear stellar disc and the contaminating bulge.

Characterization of the eclipsing post-common-envelope binary TIC 60040774

ABSTRACT Binaries with a white dwarf primary and a main sequence secondary can be used to test our understanding of both single and binary star evolution. A small fraction of such systems experienced a common-envelope phase from which they emerged with a relatively short orbital period. Here, we present the characterization of an eclipsing post-common-envelope binary of this kind, TIC 60040774, based on the light curve provided by the Transiting Exoplanet Survey Satellite (TESS), multiband photometry collated from the virtual observatory, and spectroscopic data obtained the Southern African Large Telescope (SALT). With an orbital period of 0.404807 ± 0.000149 d this system consists of a young white dwarf paired with an M6.5 dwarf companion. We estimate the masses of the primary and secondary to be 0.598 ± 0.029 M⊙ and 0.107 ± 0.020 M⊙, while the effective temperatures are 14050 ± 360 K and 2759 ± 50 K, respectively. The eclipse ingress and egress profile is shallower than expected from a simple geometric model such that more precise high-cadence photometry is required to understand the nature of this system. Given the similarity of TIC 60040774 to systems like GK Vir and NN Ser, it will be worth tracking its eclipse times to check for the presence of one or more circumbinary planets.

On the Dwarf Irregular Galaxy NGC 6822. I. Young, Intermediate, and Old Stellar Populations

We present accurate and deep multiband (g, r, i) photometry of the Local Group dwarf irregular galaxy NGC 6822. The images were collected with wide-field cameras at 2 m/4 m (INT, CTIO, CFHT) and 8 m class telescopes (Subaru) covering a 2 deg2 field of view across the center of the galaxy. We performed point-spread function photometry of ≈7000 CCD images, and the final catalog includes more than 1 million objects. We developed a new approach to identify candidate field and galaxy stars and performed a new estimate of the galaxy center by using old stellar tracers, finding that it differs by 1.′15 (R.A.) and 1.′53 (decl.) from previous estimates. We also found that young (main sequence, red supergiants), intermediate (red clump, asymptotic giant branch (AGB)), and old (red giant branch) stars display different radial distributions. The old stellar population is spherically distributed and extends to radial distances larger than previously estimated (∼1°). The young population shows a well-defined bar and a disk-like distribution, as suggested by radio measurements, that is off-center compared with the old population. We discuss pros and cons of the different diagnostics adopted to identify AGB stars and develop new ones based on optical–near-IR–mid-IR color–color diagrams to characterize oxygen- and carbon-rich stars. We found a mean population ratio between carbon and M-type (C/M) stars of 0.67 ± 0.08 (optical/near-IR/mid-IR), and we used the observed C/M ratio with empirical C/M–metallicity relations to estimate a mean iron abundance of [Fe/H] ∼ −1.25 (σ = 0.04 dex), which agrees quite well with literature estimates.

Pre-main sequence stars in LH 91

Aims. We study the accretion properties of pre-main sequence (PMS) low-mass stars in the LH 91 association within the Large Magellanic Clouds. Methods. Using optical multiband photometry obtained with the Hubble Space Telescope, we identify 75 candidates showing Hα excess emission above the 3σ level with equivalent width EWHα ⩾ 10 Å. We estimate the physical parameters (effective temperature, luminosity, age, mass, accretion luminosity, and mass accretion rate) of the PMS stellar candidates. Results. The age distribution suggests a period of active star formation ranging from a few million years up to ∼60 Myr with a gap between ∼5 Myr and 10 Myr. The masses of the PMS candidates span from 0.2 M⊙ for the cooler objects to 1.0 M⊙ with a median of ∼0.80 M⊙. The median value of the accretion luminosity of our 75 PMS stars is about 0.12 L⊙, the median value of the mass accretion rate is about 4.8 × 10−9 M⊙ yr−1 with higher values for the younger population (∼1.2 × 10−8 M⊙ yr−1), and lower values for the older candidates (∼4.7 × 10−9 M⊙ yr−1). We compare our results with findings for LH 95, the closest region to LH 91 for which accretion properties of PMS candidates were previously derived. An interesting qualitative outcome is that LH 91 seems to be in a more evolved stage. Moreover, we find that the PMS candidates are distributed homogeneously, without any evidence of clumps around more massive stars.

Investigation of stellar magnetic activity using variational autoencoder based on low-resolution spectroscopic survey

ABSTRACT We apply the variational autoencoder (VAE) to the LAMOST-K2 low-resolution spectra to detect the magnetic activity of the stars in the K2 field. After the training on the spectra of the selected inactive stars, the VAE model can efficiently generate the synthetic reference templates needed by the spectral subtraction procedure, without knowing any stellar parameters. Then, we detect the peculiar spectral features, such as chromospheric emissions, strong nebular emissions, and lithium absorptions, in our sample. We measure the emissions of the chromospheric activity indicators, Hα and Ca ii infrared triplet (IRT) lines, to quantify the stellar magnetic activity. The excess emissions of Hα and Ca ii IRT lines of the active stars are correlated well to the rotational periods and the amplitudes of light curves derived from the K2 photometry. We degrade the LAMOST spectra to simulate the slitless spectra of the China Space Station Telescope (CSST) and apply the VAE to the simulated data. For cool active stars, we reveal a good agreement between the equivalent widths of Hα line derived from the spectra with two resolutions. The result indicates the ability of identifying the magnetically active stars in the future CSST survey, which will deliver an unprecedented large data base of low-resolution spectra as well as simultaneous multiband photometry of stars.

The population of hot subdwarf stars studied with Gaia

In light of substantial new discoveries of hot subdwarfs by ongoing spectroscopic surveys and the availability of the Gaia mission Early Data Release 3 (EDR3), we compiled new releases of two catalogues of hot subluminous stars: The data release 3 (DR3) catalogue of the known hot subdwarf stars contains 6616 unique sources and provides multi-band photometry, and astrometry from Gaia EDR3 as well as classifications based on spectroscopy and colours. This is an increase of 742 objects over the DR2 catalogue. This new catalogue provides atmospheric parameters for 3087 stars and radial velocities for 2791 stars from the literature. In addition, we have updated the Gaia Data Release 2 (DR2) catalogue of hot subluminous stars using the improved accuracy of the Gaia EDR3 data set together with updated quality and selection criteria to produce the Gaia EDR3 catalogue of 61 585 hot subluminous stars, representing an increase of 21 785 objects. The improvements in Gaia EDR3 astrometry and photometry compared to Gaia DR2 have enabled us to define more sophisticated selection functions. In particular, we improved hot subluminous star detection in the crowded regions of the Galactic plane as well as in the direction of the Magellanic Clouds by including sources with close apparent neighbours but with flux levels that dominate the neighbourhood.

Asteroseismology of the multiple stellar populations in the globular cluster M4

We present a new asteroseismic analysis of the stars in the globular cluster (GC) M4 based on the data collected by the K2 mission. We report the detection of solar-like oscillation in 37 stars, 32 red giant branch (RGB) and six red horizontal branch (rHB) stars, which is the largest sample for this kind of study in GCs up to date. Combining information from asteroseismology and multi-band photometry, we estimate both the masses and the radii of our targets. Our estimates are in agreement with independent sources, serving as a crucial verification of asteroseismology in the low metallicity regime. As M4 is an old GC, it hosts multiple stellar populations differing in light element abundances and in helium mass fraction. This generates a mass difference between the populations along the RGB, which in the case of M4 is estimated to be 0.017 M⊙. With this wealth of information, we can assign population membership and estimate the average mass of the stellar populations; however, the current uncertainties do not allow us to resolve this mass difference. The population membership and the seismic data of RGB and HB stars allow us, however, to assess the integrated mass loss along the RGB of the first generation stars in the cluster. We obtain ΔM = 0.227 ± 0.028 M⊙, which is in good agreement with independent estimates. Finally, we observe the presence of a statistically significant mass-temperature gradient in the rHB stars. This represents the first direct, model-independent observation of the colour-temperature-mass correlation predicted by the theory.

Ram pressure stripping in the z ∼ 0.5 galaxy cluster MS 0451.6-0305

Context. The pressure exerted by the ambient hot X-ray gas on cluster galaxies can lead to the presence of ram pressure stripped (RPS) galaxies, characterized by asymmetric shapes, and, in some cases, tails of blue stars and/or X-ray gas, with increased star formation. Aims. With the aim of increasing the known sample of RPS galaxies at redshift z ∼ 0.5, notably higher than most RPS samples presently known, we extended our searches for such galaxies to the cluster MS 0451.6-0305. Methods. Our study is based on Hubble Space Telescope (HST) imaging in the F814W band (corresponding to a restframe wavelength of 529 nm), covering a region of about 6 × 6 Mpc2, an eight magnitude ground-based catalogue with photometric redshifts, and a spectroscopic redshift catalogue. We defined as cluster members a spectroscopic redshift sample of 359 galaxies within ±4σv of the mean cluster velocity, and a photometric redshift sample covering the [0.48, 0.61] range. We searched for RPS galaxies in the HST images and tested the error on their classification with a Zooniverse collaboration. We also computed the phase space diagram of RPS candidates in the spectroscopic sample. Finally, we ran the LePhare stellar population synthesis code through the GAZPAR interface to analyze and compare the properties of RPS and non-RPS galaxies. Results. We find 56 and 273 RPS candidates in the spectroscopic and photometric redshift samples, respectively. They are distributed throughout the cluster and tend to avoid high density regions. The phase space diagram gives the percentages of virialized, backsplash, and infall galaxies. RPS galaxy candidates typically show rather high star formation rates, young ages, and relatively low masses. We compare all our results to those previously obtained for the massive merging cluster MACS J0717+3745, at a similar redshift. Conclusions. This study increases by at least 56 objects if we only consider galaxies with spectroscopic redshifts, and probably much more if galaxies with photometric redshifts are taken into account. This study increases the number of RPS candidates at redshift z > 0.5, and confirms that they host, on average, younger stellar populations and strongly form stars when compared with non-RPS counterparts. The fact that RPS candidates with spectroscopic and with photometric redshifts have comparable properties shows that large samples of such objects could be gathered based on multi-band photometry only, a promising result in view of the very large imaging surveys planned in the coming years (DES, Euclid, LSST, etc.).

TOI-1696: A Nearby M4 Dwarf with a 3 R ⊕ Planet in the Neptunian Desert

We present the discovery and validation of a temperate sub-Neptune around the nearby mid-M dwarf TIC 470381900 (TOI-1696), with a radius of 3.09 ± 0.11 R ⊕ and an orbital period of 2.5 days, using a combination of Transiting Exoplanets Survey Satellite (TESS) and follow-up observations using ground-based telescopes. Joint analysis of multiband photometry from TESS, Multicolor Simultaneous Camera for studying Atmospheres of Transiting exoplanets (MuSCAT), MuSCAT3, Sinistro, and KeplerCam confirmed the transit signal to be achromatic as well as refined the orbital ephemeris. High-resolution imaging with Gemini/’Alopeke and high-resolution spectroscopy with the Subaru InfraRed Doppler (IRD) confirmed that there are no stellar companions or background sources to the star. The spectroscopic observations with IRD and Infrared Telescope Facility SpeX were used to determine the stellar parameters, and it was found that the host star is an M4 dwarf with an effective temperature of T eff = 3185 ± 76 K and a metallicity of [Fe/H] = 0.336 ± 0.060 dex. The radial velocities measured from IRD set a 2σ upper limit on the planetary mass to be 48.8 M ⊕. The large radius ratio (R p/R ⋆ ∼ 0.1) and the relatively bright near-infrared magnitude (J = 12.2 mag) make this planet an attractive target for further follow-up observations. TOI-1696 b is one of the planets belonging to the Neptunian desert with the highest transmission spectroscopy metric discovered to date, making it an interesting candidate for atmospheric characterizations with JWST.

Planetesimals around stars with TESS (PAST) – II. An M dwarf ‘dipper’ star with a long-lived disc in the TESS continuous viewing zone

ABSTRACT Studies of T Tauri discs inform planet formation theory; observations of variability due to occultation by circumstellar dust are a useful probe of unresolved, planet-forming inner discs, especially around faint M dwarf stars. We report observations of 2M0632, an M dwarf member of the Carina young moving group that was observed by Transiting Exoplanet Survey Satellite over two 1-yr intervals. The combined light curve contains >300 dimming events, each lasting a few hours, and as deep as 40 per cent (0.55 magnitudes). These stochastic events are correlated with a distinct, stable 1.86-d periodic signal that could be stellar rotation. Concurrent ground-based, multiband photometry show reddening consistent with interstellar medium-like dust. The star’s excess emission in the infrared and emission lines in optical and infrared spectra reveal a T Tauri-like accretion disc around the star. We confirm membership of 2M0632 in the Carina group by a Bayesian analysis of its Galactic space motion and position. We combine stellar evolution models with Gaia photometry and constraints on Teff, luminosity, and the absence of detectable lithium in the photosphere to constrain the age of the group and 2M0632 to 40–60 Myr, consistent with earlier estimates. 2M0632 joins a handful of long-lived discs which challenge the canon that disc lifetimes are ≲10 Myr. All known examples surround M dwarfs, suggesting that lower X-ray/ultraviolet irradiation and slower photoevaporation by these stars can dramatically affect disc evolution. The multiplanet systems spawned by long-lived discs probably experienced significant orbital damping and migration into close-in, resonant orbits, and perhaps represented by the TRAPPIST-1 system.

Characterization of Supernovae Based on the Spectral–Temporal Energy Distribution: Two Possible SN Ib Subtypes

A quantitative data-driven comparison among supernovae (SNe) based on their spectral time series combined with multiband photometry is presented. We use an unsupervised random forest algorithm as a metric on a set of 82 well-documented SNe representing all the main spectroscopic types, in order to embed these in an abstract metric space reflecting shared correlations between the objects. We visualize the resulting metric space in 3D, revealing strong agreement with the current spectroscopic classification scheme. The embedding splits Type Ib supernovae into two groups, with one subgroup exhibiting broader, less prominent, higher-velocity lines than the other, possibly suggesting a new SN Ib subclass is required. The method could be to classify newly discovered SNe according to their distance from known event groups, or ultimately to devise a new, spectral–temporal classification scheme. Such an embedding could also depend on hidden parameters that may perhaps be physically interpretable.

Characterizing eclipsing white dwarf M dwarf binaries from multiband eclipse photometry

ABSTRACT With the prevalence of wide-field, time-domain photometric sky surveys, the number of eclipsing white dwarf (WD) systems being discovered is increasing dramatically. An efficient method to follow these up will be key to determining any population trends and finding any particularly interesting examples. We demonstrate that multiband eclipse photometry of binaries containing a WD and an M dwarf can be used to determine the masses and temperatures of the WDs to better than 5 per cent. For the M dwarfs, we measure their parameters to a precision of better than 6 per cent with the uncertainty dominated by the intrinsic scatter of the M dwarf mass–radius relationship. This precision is better than what can typically be achieved with low-resolution spectroscopy. The nature of this method means that it will be applicable to LSST data in the future, enabling direct characterization without follow-up spectroscopy. Additionally, we characterize three new post-common-envelope binaries from their eclipse photometry, finding two systems containing hot helium-core WDs with low-mass companions (one near the brown dwarf transition regime) and a possible detached cataclysmic variable at the lower edge of the period gap.

Difference of Photometric Properties between Regular and Nonregular Miras in the Magellanic Clouds

Abstract Mira variables are asymptotic giant-branch pulsating stars with long pulsation periods and large amplitudes in optical bands. By applying the random forest algorithm to the I-band light curves for the Miras in the Magellanic Clouds, we have classified these Miras into regular Miras and nonregular Miras. Nonregular Miras exhibit a long-term variation in addition to their primary pulsation periods. Our results confirm that the period–luminosity relation for maximum light has a small dispersion, but only occurs on the regular oxygen-rich Miras, which we recommend to be applied in future distance-scale work. We have also collected multiband photometry for these Miras to perform a spectral energy distribution fitting with stellar and dust components, showing that a significant fraction of dust is present around the nonregular Miras. According to our results, we believe that the periodic long-term variations seen in the nonregular Miras might be due to the presence of dust.