Resolving the circumstellar environment of the Galactic B[e] supergiant star MWC 137, II : nebular kinematics and stellar variability

The Galactic B[e] supergiant MWC 137 is surrounded by a large-scale optical nebula. To shed light on the physical conditions and kinematics of the nebula, we analyze the optical forbidden emission lines [N II] λλ 6548,6583 and [S II] λλ 6716,6731 in long-slit spectra taken with ALFOSC at the Nordic Optical Telescope. The radial velocities display a complex behavior but, in general, the northern nebular features are predominantly approaching while the southern ones are mostly receding. The electron density shows strong variations across the nebula with values spreading from about zero to ~800 cm-3. Higher densities are found closer to MWC 137 and in regions of intense emission, whereas in regions with high radial velocities the density decreases significantly. We also observe the entire nebula in the two [S II] lines with the scanning Fabry-Perot interferometer attached to the 6 m telescope of the Special Astrophysical Observatory. These data reveal a new bow-shaped feature at P.A. = 225°-245° and a distance 80″ from MWC 137. A new Hα image has been taken with the Danish 1.54 m telescope on La Silla. No expansion or changes in the nebular morphology appear within 18.1 yr. We derive a mass of 37+9−5M⊙ and an age of 4.7 ± 0.8 Myr for MWC 137. Furthermore, we detect a period of 1.93 d in the time series photometry collected with the TESS satellite, which could suggest stellar pulsations. Other, low-frequency variability is seen as well. Whether these signals are caused by internal gravity waves in the early-type star or by variability in the wind and circumstellar matter currently cannot be distinguished. * Based on observations collected with (1) the Nordic Optical Telescope, operated by the Nordic Optical Telescope Scientific Association at the Observatorio del Roque de los Muchachos, La Palma, Spain, of the Instituto de Astrofisica de Canarias, (2) the Danish 1.54 m telescope at La Silla, Chile, and (3) the 6 m telescope of the Special Astrophysical Observatory (SAO), Russia.Fil: Kraus, Michaela. Czech Academy of Sciences; República ChecaFil: Liimets, Tiina. Czech Academy of Sciences; República ChecaFil: Moiseev, Alexei. Special Astrophysical Observatory; RusiaFil: Sánchez Arias, Julieta Paz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Nickeler , Dieter H.. Astronomický Ústav, Rep. Checa; República ChecaFil: Cidale, Lydia Sonia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Jones, D.. Instituto de Astrofisica de Canarias; Españ

Resolving the Circumstellar Environment of the Galactic B[e] Supergiant Star MWC 137 from Large to Small Scales

The Galactic object MWC 137 has been suggested to belong to the group of B[e] supergiants. However, with its large-scale optical bipolar ring nebula and high-velocity jet and knots, it is a rather atypical representative of this class. We performed multiwavelength observations spreading from the optical to the radio regimes. Based on optical imaging and long-slit spectroscopic data, we found that the northern parts of the large-scale nebula are predominantly blueshifted, while the southern regions appear mostly redshifted. We developed a geometrical model consisting of two double cones. Although various observational features can be approximated with such a scenario, the observed velocity pattern is more complex. Using near-infrared integral-field unit spectroscopy, we studied the hot molecular gas in the vicinity of the star. The emission from the hot CO gas arises in a small-scale disk revolving around the star on Keplerian orbits. Although the disk itself cannot be spatially resolved, its emission is reflected by the dust arranged in arc-like structures and the clumps surrounding MWC 137 on small scales. In the radio regime, we mapped the cold molecular gas in the outskirts of the optical nebula. We found that large amounts of cool molecular gas and warm dust embrace the optical nebula in the east, south, and west. No cold gas or dust was detected in the north and northwestern regions. Despite the new insights into the nebula kinematics gained from our studies, the real formation scenario of the large-scale nebula remains an open issue.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La PlataInstituto Argentino de Radioastronomí

Resolving the Circumstellar Environment of the Galactic B[e] Supergiant Star MWC 137 from Large to Small Scales

The Galactic object MWC 137 has been suggested to belong to the group of B[e] supergiants. However, with its large-scale optical bipolar ring nebula and high-velocity jet and knots, it is a rather atypical representative of this class. We performed multiwavelength observations spreading from the optical to the radio regimes. Based on optical imaging and long-slit spectroscopic data, we found that the northern parts of the large-scale nebula are predominantly blueshifted, while the southern regions appear mostly redshifted. We developed a geometrical model consisting of two double cones. Although various observational features can be approximated with such a scenario, the observed velocity pattern is more complex. Using near-infrared integral-field unit spectroscopy, we studied the hot molecular gas in the vicinity of the star. The emission from the hot CO gas arises in a small-scale disk revolving around the star on Keplerian orbits. Although the disk itself cannot be spatially resolved, its emission is reflected by the dust arranged in arc-like structures and the clumps surrounding MWC 137 on small scales. In the radio regime, we mapped the cold molecular gas in the outskirts of the optical nebula. We found that large amounts of cool molecular gas and warm dust embrace the optical nebula in the east, south, and west. No cold gas or dust was detected in the north and northwestern regions. Despite the new insights into the nebula kinematics gained from our studies, the real formation scenario of the large-scale nebula remains an open issue.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La PlataInstituto Argentino de Radioastronomí

Photometry of the peculiar variable V838 Mon and it's comparison stars

Lähtuvalt raskustest pekuliaarse muutliku tähe V838 Mon käitumise tõlgendamisel on oluline pidevalt täiendada kooperatiivset rahvusvahelist vaatlusandmete baasi selle objekti kohta. Fotomeetrilised aegread on andmebaasi tähtis osa. Käesolevas töös on esitatud V838 Mon heleduskõverad aastail 2002-2007, mis põhinevad Tartu Observatooriumis ja Lõuna-Aafrika Astronoomia Observatooriumis (SAAO) tehtud vaatlustel ning on töö autori panus nimetatud andmebaasi. Rõhutada võib andmete SAAO-st pärinevat osa, kus uue nähtusena on täheldatud heledusvõnkumisi, mis kaasnevad V838 Mon tagasipöördumisega stabiilsesse olekusse pärast tähekomponentide lähenemist ja kuuma komponendi varjutust 2006. a. lõpul. Uuritava objekti heleduseandmete kvaliteeti määrab kasutatava võrdlustähtede kalibreerimise täpsus. Käesoleva töö põhjal saab teha järelduse, et meie mõõtmisvigade piires on V838 Mon puhul üldkasutatavate võrdlustähtede heledus olnud konstantne ja nende standardsed heledused on määratud süstemaatilise veata. Seega on ka V838 Mon heledused juhuslike mõõtmisvigade piires usaldusväärsed

Hilises evolutsiooni faasis olevate tähtede väljapaisatud udukogud ja joad

Väitekirja elektrooniline versioon ei sisalda publikatsiooneKäesolevas doktoritöös uuritakse hilises evolutsiooni faasis olevate tähtede poolt välja paisatud ainet. Tähed on sfäärilised peaaegu kogu oma elu, aga nende elutee lõpul, kui toimuvad erinevad massikao episoodid, võtab tähtedest välja visatud aine reeglina ebaregulaarse kuju. Miks, on hetkel üks peamisi küsimusi täheümbriste valdkonnas. Täheümbrised, mida meie uurime, evolutsioneeruvad aastate, isegi kuude jooksul. See võimaldab nende arengut uurida reaalajas. Seda juhtub astronoomias harva! Aastate jooksul oleme kogunud valitud objektidest mitmetel epohhidel taevakaadreid, milledest on võimalik arvutada täheümbriste erinevate osade kiiruskomponente taevasfääril. Pilte täiendavad spektraalvaatlused, mis annavad vaatekiiresuunalise kiiruse komponendi. Pannes kolm kiiruse komponenti kokku, saame luua jäänuki reaalse 3D evolutsiooni mudeli, mis on oluline eeldus teoreetiliste mudelite jaoks.In this PhD Thesis we study the occurrence of powerful stellar outbursts in the late phases of evolution of stars like the Sun. This is one of the most controversial topics in the field, as the extraordinary variety of shapes revealed by observations are not expected to be the result of the evolution of stars that are basically spherical all over their lives. The stellar ejecta that we study occur and develop on time-scales of years, even months. This allows us to study their evolution in real-time. A very rare opportunity in Astrophysics! To this aim, we have gathered over the years a unique collection of multi epoch images, from which we produce "movies" that reveal the expansion of the nebulae as projected in the plane of the sky. Images are complemented by spectra that measure the line-of-sight velocities, also required to build 3D models of the dynamical evolution of the outflows, a privileged information for theoretical modelling.https://www.ester.ee/record=b524521

Large-Scale Ejecta of Z CMa -- Proper Motion Study and New Features Discovered

Z Canis Majoris is a fascinating early-type binary with a Herbig Be primary and a FU Orionis-type secondary. Both of the stars exhibit sub-arcsecond jet-like ejecta. In addition, the primary is associated with the extended jet as well as with the large-scale outflow. In this study, we investigate further the nature of the large-scale outflow, which has not been studied since its discovery almost three and a half decades ago. We present proper motion measurements of individual features of the large-scale outflow and determine their kinematical ages. Furthermore, with our newly acquired deep images, we have discovered additional faint arc-shaped features that can be associated with the central binary.Comment: 15 pages, 4 figures, published in Galaxie

Large-Scale Ejecta of Z CMa—Proper Motion Study and New Features Discovered

Z Canis Majoris is a fascinating early-type binary with a Herbig Be primary and a FU Orionis-type secondary. Both of the stars exhibit sub-arcsecond jet-like ejecta. In addition, the primary is associated with the extended jet as well as with the large-scale outflow. In this study, we investigate further the nature of the large-scale outflow, which has not been studied since its discovery almost three and a half decades ago. We present proper motion measurements of individual features of the large-scale outflow and determine their kinematical ages. Furthermore, with our newly acquired deep images, we have discovered additional faint arc-shaped features that can be associated with the central binary.Instituto de Astrofísica de La Plat

Near-infrared Characterization of Four Massive Stars in Transition Phases

Massive stars typically undergo short-lived post-main-sequence evolutionary phases with strong mass loss and occasional mass eruptions. Many of such massive stars in transition phases have been identified based on their dusty envelopes. The ejected material often veils the stellar photospheres so that the central stars cannot be assigned proper spectral types and evolutionary stages. The infrared spectral range has proved to be ideal for the classification of evolved massive stars and for the characterization of their environments. To improve our knowledge on the central stars of four such dust-enshrouded objects, [GKF 2010] MN 83, [GKF 2010] MN 108, [GKF 2010] MN 109, and [GKF 2010] MN 112, we collect and present their first medium-resolution K-band spectra in the 2.3-2.47 μm region and discuss the location of the stars in the JHK color-color diagram. We find that the emission-line spectra of both MN 83 and MN 112 show characteristics typically seen in luminous blue variable (LBV) stars. In addition, we propose that the presence and strength of the newly reported Mg II lines might be used as a new complementary criterion to identify LBV candidates. The spectra of the other two objects imply that MN 108 is an O-type supergiant, whereas MN 109 could be an LBV candidate in its active phase. We derive lower limits for the reddening toward the stars and find that three of all dereddened fall into the region of confirmed LBVs.Fil: Cochetti, Yanina Roxana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; Argentina. Universidad Nacional de la Plata. Facultad de Cs.astronómicas y Geofísicas. Departamento de Espectrocopia Estelar; ArgentinaFil: Kraus, Michaela. Astronomical Institute, Czech Academy Of Sciences; República ChecaFil: Arias, María Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; Argentina. Universidad Nacional de la Plata. Facultad de Cs.astronómicas y Geofísicas. Departamento de Espectrocopia Estelar; ArgentinaFil: Cidale, Lydia Sonia. Universidad Nacional de la Plata. Facultad de Cs.astronómicas y Geofísicas. Departamento de Espectrocopia Estelar; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Eenmäe, Tõnis. University Of Tartu. Faculty Of Science And Technology. Tartu Observatory.; EstoniaFil: Liimets, Tiina. University Of Tartu. Faculty Of Science And Technology. Tartu Observatory.; Estonia. Astronomical Institute, Czech Academy Of Sciences; República ChecaFil: Torres, Andrea Fabiana. Universidad Nacional de la Plata. Facultad de Cs.astronómicas y Geofísicas. Departamento de Espectrocopia Estelar; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Djupvik, Anlaug A.. Nordic Optical Telescope; Españ