Context. Understanding the formation of bound star clusters with a low star formation efficiency (SFE) is important for improving our knowledge of the star-formation history of galaxies. In N-body models of star-cluster evolution after gas expulsion, the Plummer model with an outer power law density profile has been used in a broad range of studies. Aims. Here, we study the impact of the density profile slopes on the survivability of the low-SFE star clusters after instantaneous gas expulsion. We compare cases when a stellar cluster exhibits a Plummer profile to those with Dehnen profiles, including cuspy ones of different slopes at the time of formation. Methods. We determined the corresponding density profile of the residual gas for a given global SFE, assuming that our model clusters formed with a constant efficiency per free-fall time and, hence, with a shallower density profile for the gas than that of the stars. We performed direct N-body simulations of evolution of clusters initially in virial equilibrium within the gas potential following gas removal. Results. We find that the violent relaxation lasts no longer than 20 Myr, independently of the density profile power law slopes. Dehnen model clusters survive after violent relaxation with significantly lower SFEs when the global SFE measured within the Jacobi radius or within a half-mass radius. Dehnen γ = 0 model clusters show a similar final bound fraction with the Plummer model clusters if the global SFE is measured within ten scale radii. The final bound fraction increases with the γ values for a given global SFE. Conclusions. We conclude that Dehnen clusters better resist the consequences of the violent relaxation that follows the instantaneous gas expulsion, as compared to the Plummer clusters. Therefore, the shallower the outer density slope of the low-SFE clusters, the better their prospects for survival after gas expulsion. Among the Dehnen clusters, we find that the steeper the inner slope, the higher the bound mass fraction that is retained, following the violent relaxation for a given global SFE.

We present high-angular resolution observations, conducted with the Atacama Large Millimeter/Submillimeter Array (ALMA) in Band 6, of high-excitation molecular lines of ${\mathrm{CH}}_3\mathrm{CN}$, CH₃OH, and the H29$\alpha$ radio recombination line, towards the G333.6-0.2 ultracompact (UC) H ii region. Our observations reveal three hot molecular cores: A, B, and C, where emission is detected in ten components of the $J=14\to 13$ rotational ladder of ${\mathrm{CH}}_3\mathrm{CN}$ and in the CH₃OH $J=5_{1,4}\to 4_{1,3}$ transition. Rotational diagram analysis of ${\mathrm{CH}}_3\mathrm{CN}$ reveals excitation temperatures ranging from 380 to 430 K. First-order moment maps of ${\mathrm{CH}}_3\mathrm{CN}$ and CH₃OH reveal distinct velocity gradients in all cores, suggesting rotating structures, with core A also showing evidence of expansion motions. The H29$\alpha$ recombination line shows a linewidth of $30.2\pm 0.12$ km s⁻¹, dominated by dynamical and thermal broadening, indicative of large-scale motions in ionized gas. Analysis of the ionized gas properties yields an electron density of $(4.8\pm 0.4)\times {10}^5$ cm⁻³, an emission measure of $(1.23\pm 0.06)\times {10}^9$ pc cm⁻⁶, and a Lyman continuum photon flux consistent with an O5–O6 V (Zero-Age Main Sequence; ZAMS) star. Our results suggest that G333.6-0.2 is in an intermediate evolutionary stage between hypercompact (HC) and ultracompact (UC) H ii regions, hosting active high-mass star formation with rotating hot cores and ionized gas dynamics.

With the advent of the Gaia DR2 catalog, which contains astrometric and photometric parameters for a large number of stars, measured with a high degree of accuracy, data about the cosmos and the Universe, including Star clusters in our Galaxy, are growing. However, when observed, the cluster stars are lost against the background of stars in the dense Galactic field. In addition, observational data alone is not sufficient to study real clusters from birth to destruction. In this regard, a number of numerical simulations of star clusters have been running to explain the processes and to determine the membership of cluster stars. And for this, we need to conduct a mock observation of model clusters. In this paper, we performed analyses on the output data from numerical simulations and developed a method for conducting mock observations of model clusters. We took one model of a star cluster with an age of 350 Myr, with a mass of 6000 , and with a star formation efficiency SFE=0.25, and put it in different galactic longitudes and at different distances from the Sun. In conclusion, using this method, we can put a cluster at any point on the celestial sphere, and this in turn allows you to compare with the real observed clusters and evaluate the possibility of detecting physical parameters in them. С появлением каталога Gaia DR2, содержащего астрометрические и фотометрические параметры для большого числа звезд, измеренные с высокой степенью точности, данные о космосе и Вселенной растут, в том числе данные о звездных скоплениях в нашей Галактике. Однако при наблюдении звезды скопления теряются на фоне звезд в плотном поле Галактики. Кроме того, одних наблюдательных данных недостаточно для изучения реальных скоплений от рождения до распада. В связи с этим проводится ряд численных симуляций звездных скоплений для объяснения процессов и определения принадлежности звезд скопления. А для этого нам нужно провести мнимое наблюдение за модельными кластерами. В этой статье мы провели анализ выходных данных численного моделирования и разработали метод проведения мнимых наблюдений модельных скоплений. Мы взяли одну модель звездного скопления с возрастом 350 млн лет, массой 6000 и эффективностью звездообразования SFE=0.25 и разместили ее на разных галактических долготах и ​​на разных расстояниях от Солнца. В заключение с помощью этого метода мы можем поставить скопление в любую точку небесной сферы, а это в свою очередь позволяет сравнить с реально наблюдаемыми скоплениями и оценить возможность обнаружения в них физических параметров Жоғары дәлдікпен өлшенетін, жұлдыздардың үлкен санына арналған астрометриялық және фотометриялық параметрлері бар Gaia DR2 каталогының пайда болуының арқасында, ғарыш пен Ғалам және соның ішінде, біздің Галактикадағы жұлдыз шоғырлар туралы деректер артуда. Дегенмен, Галактиканың тығыз өрісіндегі жұлдыздар фонының әсерінен бақылау кезінде шоғырлар жұлдыздары жоғалып кетеді. Сонымен қатар, нақты кластерлерді туғаннан ыдырағанға дейін зерттеу үшін тек бақылау деректері жеткіліксіз. Осыған байланысты процестерді түсіндіру және жұлдыздардың шоғырға мүшелігін анықтау үшін жұлдыз шоғырларының бірқатар сандық модельдеулері жүргізіледі. Ал ол үшін жасалған кластерлерді ойша бақылау жүргізу керек. Бұл мақалада біз сандық модельдеу нәтижелерін талдадық және модельдік кластерлердің аспан сферасында ойша бақылау әдісін әзірледік. Біз жасы 350 миллион жыл, массасы 6000 және жұлдыз түзілу тиімділігі SFE=0.25 болатын бір жұлдыз шоғырының үлгісін алып, оны әртүрлі галактикалық бойлықта және Күннен әртүрлі қашықтықта орналастырдық. Қорытындылай келе, бұл әдісті қолдана отырып, біз кластерді аспан сферасының кез келген нүктесіне орналастыра аламыз және бұл өз кезегінде нақты бақыланатын кластерлермен салыстыруға және олардағы физикалық параметрлерді бағалауға мүмкіндік береді.

We report the first detection of a magnetic field in a star of the FS CMa type, a subgroup of objects showing the B[e] phenomenon. These stars are surrounded by an extended circumstellar medium, which is responsible for emission lines from both permitted and forbidden transitions, a large infrared excess due to dust, and a very complicated variability. The split of magnetically sensitive lines in the spectra of IRAS 17449+2320 unexpectedly revealed a strong magnetic field with strength of 6.2+/-0.2 kG. Our discovery indicates the importance of considering magnetic fields in studies of FS CMa stars, whose evolutionary status is still unknown. We found that IRAS 17449+2320 has an effective temperature of ~10,000 K. Several spectral lines affected by the circumstellar medium (e.g., O I 7772–7775 AA, Balmer lines) regularly exhibit redshifted absorption components with a period of 36.13 days. The same periodicity shows up in the equivalent width of the Halpha line. The analysis of our data suggests three possible scenarios for the nature and evolutionary status of the object: i) a magnetic A-type star primary with a hot dwarf secondary, ii) a binary merger, or iii) a magnetic Ap star near the terminal age main sequence. The latter one may represent an object which has been sought for decades and fills the gap in the observations and theory of magnetic Ap stars.

Objects with the B[e] phenomenon, whose defining features are the presence of forbidden emission lines and infrared excess coming from circumstellar dust, represent a broad range of evolutionary stages from pre-main-sequence to planetary nebulae. They are important for understanding mechanisms of the circumstellar matter formation and evolution. However, it is not easy to discover them, especially among faint stars, as forbidden emission lines are usually weak and hardly noticeable in low-resolution spectra. We developed photometric criteria to search for candidate objects with this phenomenon based on a combination of optical and near-infrared color indices and found nearly 40 objects that satisfy these criteria. Spectroscopy of the candidates allows us to make more confident conclusions on their classification. We present the results of our photometric and spectroscopic observations of six objects, which are part of a large list of ∼40 objects that satisfy our photometric selection criteria for candidate objects with the B[e] phenomenon. Forbidden lines of neutral oxygen were clearly detected in the optical spectrum of one object (VES 683) and suspected in three others. One object, AS 415, is most likely a binary system with components that exhibit partial eclipses but without the B[e] phenomenon, while IRAS 20402 + 4638 may be a luminous member of the FS CMa objects group.