For several decades we have been performing photometric monitoring of some of the star formation regions using the telescopes in Rozhen Observatory. We consider that the study of photometric variability of pre-main sequence (PMS) stars is of great importance in understanding stellar evolution. A number of young stellar objects show brightness variability with large amplitudes that can be registered with small and medium-sized telescopes. But in recent years, bright traces of satellites have increasingly appeared in our CCD images. So far they are not much of a problem since most of our objects and the standard stars around them are point sources of small apparent size. But in the future, the possible increase in the number and brightness of satellite tracks may affect the quality of the photometric data we receive.

Bright satellite streaks present challenges for astronomy. No streak detection is prefect and the profile of the streak flux varies along the streak. Using Rubin Observatory’s LSST as an example, we undertake full simulations and outline the challenges and the impact on science.

The Pampilhosa da Serra Space Observatory (PASO) is located in the centre of the continental Portuguese territory, in the heart of a dark-sky destination certified by the Starlight Foundation (Aldeias do Xisto) and has been an instrumental asset to advance science, education and astrotourism certifications. PASO hosts astronomy and Space Situational Awareness (SSA) activities including a node of the Portuguese Space Surveillance & Tracking (SST) infrastructure network, such as a space radar currently in the test phase using the GEM radiotelescope, a double Wide Field of View (WFOV) Telescope system, and a European Union SST optical sensor telescope. These instruments allow surveillance of satellite and space debris in LEO, MEO and GEO orbits. The WFOV telescope offers spectroscopy capabilities enabling light curve analysis and cosmic sources monitoring. Instruments for space weather are being considered for installation to monitor solar activities and expand the range of SSA services.

Carbon-14 (14C) analysis of tree rings has revealed multiple rapid increases in 14C (14C spikes) during the Holocene, e.g., in ca. 774 CE, 993 CE, 660 BCE, and 7176 BCE. These 14C spikes have been replicated by several tree-ring 14C records and other cosmogenic nuclide records, such as 10Be and 36Cl from ice cores. These events are considered to have been caused by extreme solar energetic particle (SEP) events, with the scale of the SEP events estimated to be several dozen times larger than the largest SEP event detected in modern observations. As such, studies on past SEP events using cosmogenic nuclides have advanced in recent years; however, several issues regarding such events remain unknown. This paper reviewed recent studies on the following topics: 1) further exploration of extreme SEP events over the long term, and 2) exploration of intermediate-sized SEP events between those detected by modern observations and the extreme SEP events detected by cosmogenic nuclides. Future research directions for these topics were also discussed.

Recent research has revealed that small-scale coronal mass ejections (CMEs) in the quiet Sun exhibit similarities in their formation mechanisms and eruption characteristics when compared to large-scale solar eruptions. The occurence of small-scale CMEs increases exponentially as their size decreases. Thus, the role of small-scale CMEs in solar wind formation should not be underestimated. Can small-scale eruptions in the quiet Sun propagate into the higher solar corona? I analyze a typical small-scale eruption in the quiet Sun and reconstruct a flux-rope (FR) structure. My results indicate that torus instability of the FR can be triggered at a relatively low critical height of : 8 Mm. This suggests that the quiet Sun’s FRs can easily overcome the confinement of the low coronal magnetic field and enter the higher corona. However, further investigation is still needed to determine if the large-scale coronal mangetic fields above constrain these small-scale eruptions.

The search for extraterrestrial life, especially intelligent life, is among the most profound scientific endeavors. Although the international community achieved consensus within a few years of the launch of Sputnik on legal principles fundamental to the peaceful exploration of outer space, including the Moon and other celestial bodies, those principles did not directly address the subject of SETI. Nevertheless, principles relevant to SETI are expressed in the law of outer space, including treaties in force as well as non-binding forms of international instruments. As the search for extraterrestrial intelligent beings has developed and a myriad of issues has arisen, the relevance of many of these legal principles has become apparent.

We assess the relative strength of solar cycle (SC) 25 with respect to SCs 23 and 24 based on the abundance of halo coronal mass ejections (CMEs). We make use of the halo CME database (https://cdaw.gsfc.nasa.gov/CME_list/halo/halo.html) to compare the halo CME abundance during the first four years in each of SCs 23–25. The main result is that in several aspects such as the abundance, occurrence rate, source locations, and halo heights, halo CMEs are similar between SCs 24 and 25 but different from SC 23. This result follows from the fact that weaker cycles have low heliospheric total pressure, whose backreaction on CMEs allows them to expand more and hence enhancing the chance of becoming a halo. The solar cycle variation of halo CME properties is consistent with the precursor-based cycle prediction methods that indicate SC 25 is similar to or only slightly stronger than SC 24.

I examine the applicability of ecological concepts in discussing issues related to space environmentalism. Terms such as “ecosystem”, “carrying capacity”, and “tipping point” are either ambiguous or well defined but not applicable to orbital space and its contents; using such terms uncritically may cause more confusion than enlightenment. On the other hand, it may well be fruitful to adopt the approach of the Planetary Boundaries Framework, defining trackable metrics that capture the damage to the space environment. I argue that the key metric is simply the number of Anthropogenic Space Objects, rather than for example their reflectivity, which is currently doubling every 1.7 years; we are heading towards degree scale separation. Overcrowding of the sky is a problem astronomers and satellite operators have in common.

While Coronal Mass Ejections (CMEs) are known to be the most energetic manifestation of magnetic activity on the Sun, their stellar counterparts have remained, for the most part, elusive to our detection attempts. This situation, which is in stark contrast with the significantly enhanced observed level of flaring activity of stars, questions our understanding of the extension of the solar flare-CME connection to the stellar domain. In this presentation, I have emphasized the crucial role played by the stellar magnetic field in shaping the properties of CMEs in active stars. With the aid of state-of-the-art numerical simulations, we have explored the process of magnetic confinement of CMEs by a strong large-scale stellar magnetic field. This exploration includes multiple consequences ranging from the existence of the eruption itself, to different observational signatures emerging as this process takes place in the stellar atmosphere. These results are placed in context with our current observational knowledge of stellar CMEs and avenues are given to continue improving our understanding of these transient events on other stars.

We present the discovery of three sub-Neptune exoplanets orbiting M dwarf stars: TOI-2136 b (period 7.85 days, radius Rp = 2.19 ± 0.17R⊕, mass MP = 6.4 ± 2.4M⊕), TOI-2084 b (period 6.08 days, radius Rp = 2.47 ± 0.13R⊕), and TOI-4184 b (period 4.9 days, radius Rp = 2.43 ± 0.21R⊕). All discoveries utilized TESS data combined with ground-based follow-up observations for confirmation. The location of these planets near the “radius valley” suggests diverse planetary formations around low-mass stars and holds promise for future atmospheric characterization with instruments like JWST.

Our study analyzes nearby (within 33 pc) K dwarf stars to determine their stellar properties, activity levels, kinematics, and estimated ages, as part of the RKSTAR (RECONS K Star) Survey encompassing about 5000 K dwarf primaries within 50 pc. Utilizing high-resolution spectra from the CHIRON echelle spectrometer, we established a benchmark set of 35 K dwarfs aged 20 Myr to 5 Gyr, focusing on the Hα (6563 Å) and Li I (6707.9 Å) lines. We extended our analysis to 615 K dwarfs within 33 pc and found that about 8% exhibit spectroscopic features characteristic of young or active stars. As expected, Galactic UVW space motions indicate that most of the stars fall into the thin (80%) and thick (20%) disk populations, with a single outlier, HD 134439, which is a known halo star. Additionally, 4% of the stars were identified as metal-poor ([Fe/H] ≤ −0.5 dex). This work identifies 500 inactive and mature K dwarfs as prime targets for detecting terrestrial planets and serves as a vital resource for assessing host star suitability for exoplanet habitability.

The contention of this paper is that alien visitation claims are a societal problem when they (a) move into the mainstream of discourse to the extent that government policy has to respond to them; (b) when they generate background noise which impedes science communication; and (c) when they become entangled with indigenous origin narratives, making it hard to recover the latter. Where this is the case, periodic debunking looks like a failed paradigm. Something closer to a scientific research program (SRP) might be called for, at some point. This is an idea which has already been advanced by Avi Loeb and Martin Elvis (albeit in significantly different ways and for different reasons). It is not clear that we are already at the stage where an SRP is required, but such a requirement does seem to be on the near horizon.) The paper concludes by setting out a number of framing requirements for any such SRP.

We present a solution of a devil’s advocate to put telescopes in space, as one possible way to mitigate the impact on astronomy and on the night sky of recent large satellite constellations. The limitations of telescopes in space versus on Earth are noted. However, the solution draws from the history of telescopes that had to be moved from major human settlements to rural areas in the past; and it poses que question if it is possible that the future may lead to similar moves of putting telescopes in space, as satellites become a major human development similar to human development of cities that pushed telescopes out of cities to rural areas in the past.

Infrared observations with JWST open up a new window into the chemical composition of the gas in the inner disk (<few au) where planets are built. Results from the MIRI GTO program MINDS are presented for several disks around T Tauri and lower-mass stars. A large diversity in spectra is found. Some disks are very rich in H2O lines whereas other disks show prominent CO2. The spectra of disks around very low-mass stars (<0.3 M⊙, late-M type stars like Trappist-1) are dominated by C2H2 and other hydrocarbon features including those of benzene, suggesting volatile C/O>1. Together these data point to a rich chemistry in the inner regions that is linked to the physical structure of these disks (e.g., dust traps) and that may be affected by processes such as radial drift of icy pebbles from the outer to the inner disk.

Radio observations have the potential advantage to provide not only direct confirmation about the occurrence of stellar CMEs, but are also a potential tool to probe the systematic properties of stellar CMEs. I will describe the rationale behind using radio observations to probe the incidence and properties of stellar CMEs. I’ll start with a brief review of solar radio emissions related to CMEs, then switch to observational attempts to identify stellar type II bursts, which so far have resulted in no confident detections. I will step through the several assumptions made regarding stellar type II bursts and examine their astrophysical significance. I’ll then pan out to consider other possibilities in the radio domain such as type IV bursts and negative radio bursts, and end with some perspective on future opportunities for making progress in studying stellar CMEs using radio observations.

The type-IV bursts, associated with coronal mass ejections (CMEs), occasionally extend to the decameter-hectrometric (DH) range. We present a comprehensive catalog of simultaneous multi-vantage point observations of DH type-IV bursts by Wind and STEREO spacecraft since 2006. 73% of the bursts are associated with fast (>900 km s-1) and wide (>60°) CMEs, which are mostly geoeffective halo CMEs. Also, we find that the bursts are best observed by the spacecraft located within |60°| line of sight (LOS), highlighting the importance of LOS towards active latitudes while choosing target stars for a type-IV search campaign. In young active M dwarfs, CME-associated bursts have remained elusive despite many monitoring campaigns. We present the first detection of long-duration type-III, type-IV, and type-V bursts during an active event in AD Leo (M3.5V; 0.4M☉). The observed burst characteristics support a multipole model over a solar-like active region magnetic field profile on the star.

Before a dozen years ago, we believed that the Sun is a mildly active star unable to produce disastrous events. However, as discovered in 2012, extreme events can be produced by the Sun rarely on the millennial timescales. These events include extreme solar particle events with enormous fluxes of solar energetic particles as known from cosmogenic-isotope proxies recorded in independently dateable natural archives like tree rings and polar ice cores; and super-flares as known from an analysis of thousands of sun-like stars observed recently by the space-borne telescope Kepler. While both types of events imply that the Sun can rarely produce eruptive events several orders of magnitude stronger than those we observed during the last decades, the statistics of the two types of events mismatch quantitatively. Here, we briefly summarize the start-of-the-art knowledge of the extreme events updating more detailed recent reviews and listing the open questions still remaining to be answered.