Promocijas darbs

Elektroniskā versija nesatur pielikumusRestaurētie Irbenes radioteleskopi tika pielāgoti kosmisko māzeru novērojumiem. Tika ieviesta četru soļu frekvences nobīdes metode un izstrādāts datorprogrammu kopums datu reducēšanai. Autors apkopoja metanola māzeru monitoringa rezultātus piecos gados, iegūstot 42 avotu mainīguma laika rindas. Tika konstatēti visi būtiskākie mainīguma veidi ar ļoti dažādām relatīvajām plūsmas izmaiņu amplitūdām. Kā arī 3 avotiem pirmoreiz konstatēja periodiskas plūsmas svārstības. Autors pieteica un guva iespēju novērot avotus ar Eiropas VLBI tīklu, iegūstot to loka milisekundes izšķirtspējas attēlus, 2 avoti ar šādu izšķirtspēju tika novēroti pirmoreiz. Iegūtie attēli atklāj ilgi pastāvošus māzeru mezglus, kas kontekstā ar laika sērijām, norāda uz atbalstu hipotēzei par mainīguma saistību ar izmaiņām pumpējošā starojuma intensitātēIrbene radio telescopes were adapted for cosmic maser observations, introducing a four-step frequency shift method and developing computer programs for data reduction. The author compiled the results of methanol maser monitoring over 5 years, obtaining a time series of variability for 42 sources. All significant types of variability were identified with highly diverse amplitude changes. Additionally, periodic flux oscillations were detected for 3 sources for the first time. The author obtained the opportunity to observe sources with the European VLBI Network, obtaining milliarcsecond resolution images, with 2 sources observed for the first time. The obtained images show long-existing maser cloudlets, which, in the context of time series, support the hypothesis of a connection between variability and changes in pumping radiation intensity

The methanol emission in the J1−J0J_1-J_0 A−+^{-+} line series as a tracer of specific physical conditions in high-mass star-forming regions

We present results of the investigations of the properties of the methanol $J_1 - J_0$ A$^{-+}$ line series motivated by the recent serendipitous detection of the maser emission in the $14_1 - 14_0$ A$^{-+}$ line at 349~GHz in S255IR-SMA1 soon after the accretion burst. The study includes further observations of several lines of this series in S255IR with the SMA, a mini-survey of methanol lines in the 0.8 mm range toward a sample of bright 6.7~GHz methanol maser sources with the IRAM-30m telescope, and theoretical modeling. We found that the maser component of the $14_1 - 14_0$ A$^{-+}$ line in S255IR decayed by more than order of magnitude in comparison with that in 2016. No clear sign of maser emission is observed in other lines of this series in the SMA observations except the $7_1 - 7_0$ A$^{-+}$ line where an additional bright component is detected at the velocity of the maser emission observed earlier in the $14_1 - 14_0$ A$^{-+}$ line. Our LVG model constrains the ranges of the physical parameters that matches the observed emission intensities. No obvious maser emission in the $J_1 - J_0$ A$^{-+}$ lines was detected in the mini-survey of the 6.7~GHz methanol maser sources, though one component in NGC7538 may represent a weak maser. In general, the maser effect in the $J_1 - J_0$ A$^{-+}$ lines may serve as a tracer of rather hot environments and in particular luminosity flaring events during high mass star formation.Comment: 16 pages, 12 figure

Recent updates on the Maser Monitoring Organisation

The Maser Monitoring Organisation (M2O) is a research community of telescope operators, astronomy researchers and maser theoreticians pursuing a joint goal of reaching a deeper understanding of maser emission and exploring its variety of uses as tracers of astrophysical events. These proceedings detail the origin, motivations and current status of the M2O, as was introduced at the 2021 EVN symposium

Modelling the absorption spectrum of star BS17569-0011

Veikta zvaigznes BS17569–0011 analīze izmantojot augstas izšķirtspējas absorbcijas spektru un atmosfēru modeļu metodi. Literatūrā zvaigzne klasificēta kā Galaktikas vecākās paaudzes zvaigzne ar ļoti zemu metālu koncentrāciju atmosfērā un anomālu enerģijas sadalījumu spektrā. Veikta zvaigznes integrālā starojuma analīze un konstatēts mainīgums ar dominējošo periodu, P ~ 50–75 dienas. BS17569–0011 spektrā tika identificētas ļoti intensīvas TiO molekulas absorbcijas līnijas, kas liecina par oglekļa un skābekļa attiecību C/O < 1, un emisija Balmera H un H līnijās, kas norāda uz masas zaudēšanas procesiem. Darbā noteikts zvaigznes masas centra radiālais ātrums, precizēta efektīvā temperatūra, virsmas gravitācija, mikroturbulences ātrums un aprēķināta 23 ķīmisko elementu koncentrācijas atmosfērā. Aprēķinātie atmosfēras parametri ir raksturīgi aukstajām zvaigznēm ar plašām un retinātām atmosfērām, Teff = 3300 K, log(g) = 0.0 (cgs), = 3.0 km/s.During this scientific work star’s BS17569-0011 analysis was performed using absorption spectrum and atmospheric model method. Available data classifies it as a older generation star with very low metal abundance in the atmosphere and anomalous spectral energy distribution. Stars integral radiation analysis shows variability with a characteristic period P ~ 50-90 days. BS17569 – 0011 spectrum analysis identified intense TiO lines suggesting that carbon and oxygen ratio is C/O < 1, and Balmer H and H lines emission indicate a mass loss process. Extracted data shows star’s mass center radial velocity, clarifies atmospheric effective temperature, surface gravity, microturbulent velocity and abundances of twenty chemical elements. Atmospheric parameters are typical of very cold stars with wide and tenuous atmospheres, Teff = 3300 K, log (g) = 0.0 (cgs), = 3.0 km / s. Model calculations shows that iron group elements abundance in studied star`s atmosphere is average 4 times lower

High-resolution spectroscopy of star BS17569-0011

Veikta augstas izšķirtspējas absorbcijas spektra analīze zvaigznei BS17569-0011, kas literatūrā ir klasificētā kā metālnabadzīga vecākās paaudzes zvaigzne ar anomālu enerģijas sadalījumu spektrā. Noteikts masas centra radiālas ātrums, atmosfēras efektīvā temperatūra, virsmas gravitācija, mikroturbulences ātrums un piecu ķīmisko elementu koncentrācijas. Zvaigznes spektrā identificētas intensīvas TiO līnijas un emisija Balmera H līnijā. Atmosfēras parametri ir tipiski sarkanajiem milžiem, Teff = 4250 K, log(g)=1,0 (cgs), = 3,0 km/s. Dzelzs atomu koncentrācija pētāmās zvaigznes atmosfērā ir apmēram 16 reizes zemāka nekā Saules atmosfērā. Elementu koncentrācijas, kas veidojas neitronu satveršanas procesos, ir relatīvi paaugstināta apmēram 10 reizes. Iegūtie rezultāti liecina, ka BS17569-0011 pieder Galaktikas II populācijas zvaigznēm un atrodas sarkanā milža evolūcijas stadijā. Atslēgvārdi: BS17569-0011 – atmosfēras ķīmiskais sastāvs – augstas izšķirtspējas spektroskopija – zvaigžņu evolūcija – atmosfēru modeļu metode.During this scientific work high-resolution absorption spectrum analysis of the star BS17569-0011 was performed. Available data classifies it as a metal-poor older generation star with anomalous spectral energy distribution. Extracted data also shows systemic radial velocity, atmospheric effective temperature, surface gravity, microturbulent velocity and abundances of five chemical elements. Star`s spectrum analysis identified intense TiO lines and Balmer H line emission. Atmospheric parameters are typical of red giants, Teff = 4250 K, log (g) = 1.0 (cgs), = 3.0 km / s. Abundance of iron atoms in the current star`s atmosphere is about 16 times lower than in the Solar atmosphere. Element abundances formed neutron capture processes are relatively high, about 10 times higher. The data shows that the BS17569-0011 belongs to the Galactic halo population and red giant branch evolution phase. Key words: BS17569-0011 – atmospheric chemical composition – stellar evolution – high-resolution spectrum analysis – atmospheric model method

Millimeter methanol emission in the high-mass young stellar object G24.33+0.14

In 2019 September, a sudden flare of the 6.7 GHz methanol maser was observed toward the high-mass young stellar object (HMYSO) G24.33+0.14. This may represent the fourth detection of a transient mass accretion event in an HMYSO after S255IR NIRS3, NGC 6334I-MM1, and G358.93−0.03-MM1. G24.33+0.14 is unique among these sources as it clearly shows a repeating flare with an 8 yr interval. Using the Atacama Large Millimeter/submillimeter Array (ALMA), we observed the millimeter continuum and molecular lines toward G24.33+0.14 in the pre-flare phase in 2016 August (ALMA Cycle 3) and the mid-flare phase in 2019 September (ALMA Cycle 6). We identified three continuum sources in G24.33+0.14, and the brightest source, C1, which is closely associated with the 6.7 GHz maser emission, shows only a marginal increase in flux density with a flux ratio (Cycle 6$/$Cycle 3) of 1.16 ± 0.01, considering an additional absolute flux calibration uncertainty of $10\%$. We identified 26 transitions from 13 molecular species other than methanol, and they exhibit similar levels of flux differences with an average flux ratio of 1.12 ± 0.15. In contrast, eight methanol lines observed in Cycle 6 are brighter than those in Cycle 3 with an average flux ratio of 1.23 ± 0.13, and the higher excitation lines tend to show a larger flux increase. If this systematic increasing trend is real, it would suggest radiative heating close to the central HMYSO due to an accretion event which could expand the size of the emission region and/or change the excitation conditions. Given the low brightness temperatures and small flux changes, most of the methanol emission is likely to be predominantly thermal, except for the 229.759 GHz (8−1–70 E) line known as a class I methanol maser. The flux change in the millimeter continuum of G24.33+0.14 is smaller than in S255IR NIRS3 and NGC 6334I-MM1 but is comparable with that in G358.93−0.03-MM1, suggesting different amounts of accreted mass in these events

Millimeter methanol emission in the high-mass young stellar object G24.33+0.14

&lt;jats:title&gt;Abstract&lt;/jats:title&gt; &lt;jats:p&gt;In 2019 September, a sudden flare of the 6.7???GHz methanol maser was observed toward the high-mass young stellar object (HMYSO) G24.33+0.14. This may represent the fourth detection of a transient mass accretion event in an HMYSO after S255IR??NIRS3, NGC??6334I-MM1, and G358.93???0.03-MM1. G24.33+0.14 is unique among these sources as it clearly shows a repeating flare with an 8???yr interval. Using the Atacama Large Millimeter/submillimeter Array (ALMA), we observed the millimeter continuum and molecular lines toward G24.33+0.14 in the pre-flare phase in 2016 August (ALMA Cycle??3) and the mid-flare phase in 2019 September (ALMA Cycle??6). We identified three continuum sources in G24.33+0.14, and the brightest source, C1, which is closely associated with the 6.7???GHz maser emission, shows only a marginal increase in flux density with a flux ratio (Cycle??6$/$Cycle??3) of 1.16 ?? 0.01, considering an additional absolute flux calibration uncertainty of $10\%$. We identified 26 transitions from 13 molecular species other than methanol, and they exhibit similar levels of flux differences with an average flux ratio of 1.12 ?? 0.15. In contrast, eight methanol lines observed in Cycle??6 are brighter than those in Cycle??3 with an average flux ratio of 1.23 ?? 0.13, and the higher excitation lines tend to show a larger flux increase. If this systematic increasing trend is real, it would suggest radiative heating close to the central HMYSO due to an accretion event which could expand the size of the emission region and/or change the excitation conditions. Given the low brightness temperatures and small flux changes, most of the methanol emission is likely to be predominantly thermal, except for the 229.759???GHz (8???1???70??E) line known as a class??I methanol maser. The flux change in the millimeter continuum of G24.33+0.14 is smaller than in S255IR??NIRS3 and NGC??6334I-MM1 but is comparable with that in G358.93???0.03-MM1, suggesting different amounts of accreted mass in these events.&lt;/jats:p&gt