The Central Molecular Zone (CMZ) in the Galactic Center region shows outstanding non-circular motion unlike the Galactic disk. While several models describing this non-circular motion have been proposed, a uniform kinematic model of the CMZ orbit has not yet emerged. To uncover the dynamics of the Galactic center region, we conducted VLBI astrometric observations of 22GHz water maser sources towards the Galactic center using VERA. By measuring parallaxes and proper motions, we can determine whether each source is actually located in the CMZ or not, and identify the three-dimensional positions and velocities in the non-circular orbit if the source is indeed located in the CMZ. We present the results of our astrometric study for several maser sources associated with molecular clouds towards the Galactic center. The astrometric observations toward Sgr B2(M) indicated that Sgr B2 complex is moving toward the positive Galactic longitude relative to Sgr A*.

Galaxy-galaxy strong lensing systems have been used in literature to test General Relativity by constraining the post-Newtonian parameter (γPPN). Nevertheless, these methods are prone to systematic errors, some of which arise from difficulties in modelling the dynamics of the lens galaxy. In this study, we address the systematic error related to the assumption of a constant anisotropy between the radial and tangential components of the velocity dispersion of stars within the lens galaxy, characterised by the parameter β. We considered two radial models for the anisotropy parameter, the Osipkov-Merritt and Mamon & Lokas, as well three Gaussian priors for constant β. Our analysis showed that the choice of β has a strong impact on the value of γPPN, with radial models leading to lower values of this parameter.

The Central Molecular Zone (CMZ) makes up roughly the inner 500 pc of the Milky Way and has a large amount of dense hot gas, strong magnetic fields, and highly energetic particles. The Survey of Water and Ammonia in the Galactic Center (SWAG) is a major imaging line survey using the Australia Telescope Compact Array with the goal to map out the molecular content in the entire CMZ. SWAG data includes the 22 GHz H2O maser transition which is typically used as a tracer for phases of star formation, including both young stellar objects (YSOs) and evolved stars, such as asymptotic giant branch (AGB) stars. The SWAG H2O survey is significantly deeper with better resolution than existing surveys that cover the entire CMZ. The goal is to create a robust catalog of the maser positions, spectral properties, and the sources they trace. The H2O maser catalog shows 703 H2O masers which increases the amount of detected H2O masers in the CMZ by more than an order of magnitude. The H2O masers have a more symmetric distribution in the Galactic center than that of the gas. Cross-correlation with other observations and catalogs will provide information relating maser properties to YSOs and AGB stars, for which multiple maser components will provide outflow properties. We will also connect the surrounding molecular gas to the YSO maser velocities.

The signatures of small-scale features in the solar atmosphere are severely degraded by limited angular resolution of the observations. The Deep Solar ALMA Neural Network Estimator (Deep-SANNE) is trained towards synthetic observables from 3D magnetohydrodynamic simulations to recognize the small-scale dynamic features in data at limited observational resolution, and provide maps of correction factors across the field of view. The correction factors can be used to acquire deconvolved refined images with significantly improved brightness temperature contrasts, where the strength of brightening events are reproduced to an accuracy of 94.0% instead of the 43.7% at observational resolution. Deep-SANNE can also provide masks of the most probable locations with large accuracies, and estimations on the radiation formation heights in connection to the small-scale features. The Deep-SANNE refined images and estimations of radiation formation heights allow for larger accuracy and meaningful analysis of solar ALMA data.

The instability strip (IS) of classical Cepheids has been extensively studied theoretically. Comparison of the theoretical IS edges with those obtained empirically, using the most recent Cepheids catalogs available, can provide us with insights into the physical processes that determine the position of the IS boundaries. We investigate the empirical positions of the IS of the classical Cepheids in the Large Magellanic Cloud (LMC) using data of classical fundamental-mode and first-overtone LMC Cepheids from the OGLE-IV variable star catalog, together with a recent high-resolution reddening map from the literature. We studied their position on the Hertzsprung-Russell diagram and determined the IS borders by tracing the edges of the color distribution along the strip. We obtain the blue and red edges of the IS in V- and I-photometric bands, in addition to Teff and log L⊙. The results obtained show a break located at the Cepheids’ period of about 3 days, which was not reported before. This phenomenon is most likely explained by the depopulation of second and third crossing classical Cepheids in the faint part of the IS, since blue loops of evolutionary tracks in this mass range do not extend blueward enough to cross the IS at the LMC metallicity. Furthermore, our empirical borders show good agreement with theoretical ones published in the literature. This proves that our empirical IS is a useful tool to put constraints on theoretical models.

Red supergiants (RSGs) are the brightest stars in the near-infrared. The existence of their period-luminosity relation (PLR) will be very helpful in determining cosmological distances. This review discusses the development in identification of RSGs, calculation of their light variation period, determination of the PLR, and the uncertainties associated. It is found that the PLR of RSGs exhibits the smallest scatter in the near-infrared, in particular within the P – MK relation. The PLRs in the LMC, SMC, M31, and M33 show no obvious dependence on the galactic metallicity, which follows approximately the relation as MK ≈ −3.1 log P – 1.9.

Large scale optical and infrared surveys have revealed numbers of accretion-derived stellar features within the halo of the Galaxy. These coherent tail-like features are produced by encounters with satellite dwarf galaxies. We conducted an SiO and H2O maser survey towards O-rich AGBs towards the orbital plane of the Sgr Stellar Stream from 2016. Up to now, maser emissions have been found from 60 sources, most of which are detected for the first time. However, their distances and kinematics suggest they are still disk stars.

The lightcurves of strongly lensed AGNs get distorted due to gravitational microlensing, which differently magnifies the emission regions of AGNs depending on their size. This effect has been used to measure the size of the AGN accretion disc, but high photometric accuracy lightcurves reveal coherent variations on short time-scales that are not expected by standard accretion disc models. I show that this signal can be produced by emission from the Broad Line Region (BLR) but also by extended (diffuse) continuum emission. I explain how these features can be used to measure the size of the BLR but also reveal additional sources of emission. The multi-colour lightcurves of lensed AGNs, such as those to be obtained with the Vera Rubin Observatory, may become a powerful new tool to reveal the sub-parsec structure of AGNs, and shed light on elusive AGN emitting regions such as the one producing diffuse continuum emission.

In the past decade, submillimeter surveys have been employed to define samples of gravitationally-lensed dusty star-forming galaxies (DSFGs) at z ∼ 1 − 4. These extreme objects () appear to form stars prodigiously at rates of . Using all-sky Planck and WISE surveys, and wide-area Herschel surveys, we have identified the PASSAGES sample, with some of the rarest hyper-luminous IR galaxies ever discovered. We have found that their globally-averaged star formation surface densities are always sub-Eddington, typically by an order of magnitude. This may suggest that our understanding of how radiation pressure from massive stars disrupts the collapse of molecular clouds (thereby quenching star formation) is flawed—or simply that smaller physical resolutions are necessary. With the aid of lensing, we can now capture the source-plane distribution of star formation at ∼ 100pc scales, letting us identify isolated super-Eddington regions where quenching is occurring.

Over the past 20 years, the Galactic plane has been surveyed at high resolution at wavelengths from 1 micron through to 20 cm. The combination of these surveys has produced large samples of deeply embedded young stars located across the Galactic disc. These continuum surveys are complemented by spectral line surveys of thermal, radio recombination, and molecular maser (OH, H2O, CH3OH) lines. The identified sources cover the whole range of evolutionary stages in the star formation process, allowing the physical properties of these stages to be measured. This information has been used to calculate the star formation efficiency and star formation rate of the Milky Way and to evaluate the impact of environment and location within the disc. This review provides an overview of some of the most significant studies in recent years and discusses how the evolutionary sequence has been used to investigate the correlation of other star formation tracers and maser associations.

Long-period variables are bright, evolved red giant stars showing periodic photometric changes due to stellar pulsation. They follow one or more period-luminosity and period-age relations, which make them highly promising distance indicators and tracers of young and intermediate-age stellar populations. Such a potential is especially interesting in view of the massive amount of data delivered by modern large-scale variability surveys. Crucially, these applications require a clear theoretical understanding of pulsation physics in connection with stellar evolution. Here, I describe an ongoing effort from our collaboration dedicated to the modelling of stellar pulsation in evolved stars, and how this work is impacting our capability of investigating long-period variables and exploiting them for other astrophysical studies. Furthermore, I present our ongoing work aimed at assessing the potential of semi-regular variables, an often neglected sub-type of long-period variables, to be distance indicators complementary to their better-known, more evolved counterparts, the Mira variables.

The gravitational lens SDSS J1004+4112 was the first discovered system where a background quasar is lensed by a galaxy cluster instead of a single galaxy. We use the 14.5-year r-band light curves together with the recently measured time delay of the fourth brightest quasar image (Munõz et al. (2022)) and the mass model from Forés-Toribio et al. (2022) to study the microlensing effect in this system. We constrain the quasar accretion disk size to light-days at 2407Å in the restframe which is compatible with most previous estimates. We also infer the fraction of mass in stars at the positions of the quasar images: $${\alpha _A} = 0.058_{ - 0.032}^{ + 0.024},{\alpha _B} = 0.048_{ - 0.014}^{ + 0.032},{\alpha _C} = 0.018_{ - 0.018}^{ + 0.015}$$ and $${\alpha _D} = 0.008_{ - 0.008}^{ + 0.033}$$. The stellar fraction estimates are reasonable for intracluster medium although the stellar fractions at images A and B are slightly larger, suggesting the presence of a near undetected galaxy.

In the last five years, the number of periodic variable stars has increased by two million. We used the ZTF DR2 data to find and build a catalog that includes 780,000 periodic variable stars. These periodic variable stars were classified into 11 types, which greatly complemented the variable stars in Galactic disk. Based on the latest ZTF DR16 data, we found 2 million variable candidates. We trained a machine learner to classify variable stars, and the learner had a prediction accuracy of 94%. Using millions of variable stars, we carried out studies to optimize the period–luminosity relations and the Galactic structure and the extinction law. With the future China Space Station Telescope, millions of variable stars in the Local Group will be discovered. They help to study the structure of our Local Group and also to cross-check the distance ladders based on different variable stars.

Recently, remarkable progress has been made in understanding the formation of high mass stars. Observations provided direct evidence that massive young stellar objects (MYSOs), analogously to low-mass ones, form via disk-mediated accretion accompanied by episodic accretion bursts, possibly caused by disk fragmentation. In the case of MYSOs, the mechanism theoretically provides a means to overcome radiation pressure, but in practice it is poorly studied - only three accretion bursts in MYSOs have been caught in action to date. A significant contribution to the development of the theory has been made with the study of masers, which have proven to be a powerful tool for locating “bursting” MYSOs. This overview focuses on the exceptional role that masers play in the search and study of accretion bursts in massive protostars.

We aim to uncover the structure of the continuum and broad emission line (BEL) emitting regions in the gravitationally lensed quasar SDSS J1004+4112 through unique microlensing signatures. Analyzing 20 spectroscopic observations from 2003 to 2018, we study the striking deformations of various BEL profiles and determine the sizes of their respective emitting regions. We use the emission line cores as a baseline for no microlensing and then apply Bayesian methods to derive the sizes of the Lyα, Si IV, C IV, C III], and Mg II emitting regions, as well as of the underlying continuum-emitting sources. We find that the sizes of the emitting regions for the BELs are a few light-days across, notably smaller than in typical lensed quasars. The asymmetric distortions observed in the BELs suggest that the broad-line region lacks spherical symmetry and is likely confined to a plane. The inferred continuum emitting region sizes are larger than predictions based on standard thin-disk theory by a factor of ∼ 4. We find that the size-wavelength relation is in agreement with that of a geometrically thin and optically thick accretion disk.

The protostellar environment where young stars form has physical conditions suitable to excite a number of molecular maser lines that have traditionally provided an unique probe of star formation kinematics, at the highest angular resolution of radio very long baseline interferometry (VLBI) observations. In the following, we will discuss a number of recent results on our understanding of the gas dynamics traced by masers in the vicinity of young forming stars. These findings provide direct clues on how our community can substantially contribute to the field of star formation in the next decade.