Examinando por Autor "Kurtev, Radostin"

Mostrando 1 - 3 de 3
  • Miniatura
    Ítem
    Assessing the Stellar Population and the Environment of an HII Region on the Far Side of the Galaxy
    (American Astronomical Society (Aas), 2021) Chené, André-Nicolas; Benjamin, Robert A.; Ramírez-Alegría, Sebastian; Borissova, Jura; Kurtev, Radostin; Moni Bidin, Christian; Mauro, Francesco; Lucas, Phil; Guo, Zhen; Smith, Leigh C.; Gonzalez-Fernandez, Carlos; Ivanov, Valentin D.; Minniti, Dante; Anderson, Loren. D.; Armentrout, William. P.; Gonzalez, Danilo; Herrero, Artemio; Peña Ramírez, Karla
    We have investigated the stellar and interstellar content of the distant star formation region IRAS 17591-2228 (WISE H ii region GAL 007.47+0.06). It is associated with a water maser, whose parallax distance is $d={20.4}_{-2.2}^{+2.8}$ kpc, supported by independent measurements of proper motion and radial velocity. It is projected in the same direction as an extremely red (J−KS ∼ 6 mag) group of stars, and a shell of mid-infrared emission. We qualify the group of stars as a cluster candidate, VVV CL177. Its radius spans between 0farcm45 and 1' and contains at least two young stellar objects with an extreme extinction near ${A}_{{\rm{V}}}\sim 40$ mag. Yet more analysis will be required to determine if it is a real single cluster associated with the water maser. The 13CO emissions at the radial velocity of the maser corresponds to the mid-infrared emission.
  • Miniatura
    Ítem
    Identifying and characterising post-encounter disintegrating system
    (Universidad de Valparaíso, 2023-07) Ka Po Yip, Alexandra; Kurtev, Radostin
    Disintegrating multiple systems are thought to be very common based on numerical simulations, which predict that 50% to 95% of non-hierarchical triple systems and 10% of hierarchical triple systems undergo an ejection at some point in their evolution. However, very few of these systems have so far been observed. Kinematic studies of the Hipparcos catalogue have revealed only 10 disintegrating triple candidates. They are presumably the result of dynamical encounters taking place in the Galactic disk between single/multiple systems. In this thesis, I expanded the search for such systems to study their properties, as well as to characterize possible low-mass ejecta (i.e. brown dwarfs and planets). I have assembled a list of 20 candidate systems using astrometry from the Tycho-Gaia astrometric solution (later upgraded with Gaia DR3), and here I present the follow-up of 9 of them. I have obtained medium-resolution spectra for 4 of them and used the spectra to determine their radial velocity and metallicity. These measurements allowed me to conclude that two of the systems observed with ISIS are likely genuine disintegrating systems, for which I have reconstructed the most probable interaction scenario. I have obtained DECam imaging for 5 systems and by combining near-infrared photometry and proper motion, I searched for ultra- cool ejected components. I found that the system consisting of TYC 7731-1951-1, TYC 7731-2128-1 AB, and TYC 7731-1995-1ABC?, contains one very promising ultra-cool dwarf candidate. Using additional data from the literature, I have found that 3 out of the 5 disintegrating system candidates observed with DECam are likely to be true dis- integrating systems. Overall, this thesis demonstrates the feasibility of searching for disintegrating multiple systems with the method described, as well as the feasibility of identifying additional low-mass ejected components. Future Gaia data releases and upcoming large area near-infrared surveys and new space telescopes (e.g. LSST, EU- CLID, SPHEREX, NEOSurveyor) will enable me to search for even larger samples of disintegrating systems and more low-mass ejecta. This population will be fundamental to observationally constrain the rate at which this type of systems interact in the Galactic disk. The fundamental importance of searching for possible disintegrating multiple systems is its contribution in providing further constraints to the formation models of binaries and multiple systems and their evolution.
  • Miniatura
    Ítem
    Weather on Other Worlds. VI. Optical Spectrophotometry of Luhman 16B Reveals Large-amplitude Variations in the Alkali Lines
    (American Astronomical Society, 2021) Heinze, A. N.; Metchev, Stanimir; Kurtev, Radostin; Gillon, Michael
    Using a novel wide-slit, multiobject approach with the GMOS spectrograph on the 8 m Gemini South telescope, we have obtained precise time-series spectrophotometry of the binary brown dwarf Luhman 16 at optical wavelengths over two full nights. The B component of this binary system is known to be variable in the red optical and near-infrared with a period of 5 hr and an amplitude of 5%–20%. Our observations probe its spectrally resolved variability in the 6000–10000 Å range. At wavelengths affected by the extremely strong, broadened spectral lines of the neutral alkali metals (the potassium doublet centered near 7682 Å and the sodium doublet at 5893 Å), we see photometric variations that differ strikingly from those of the 8000–10000 Å "red continuum" that dominates our detected flux. On UT 2014 February 24, these variations are anticorrelated with the red continuum, while on February 25 they have a large relative phase shift. The extent to which the wavelength-dependent photometric behavior diverges from that of the red continuum appears to correlate with the strength of the alkali absorption. We consider but ultimately reject models in which our observations are explained by lightning or auroral activity. A more likely cause is cloud-correlated, altitude-dependent variations in the gas-phase abundances of sodium and potassium, which are in chemical equilibrium with their chlorides in brown dwarf atmospheres. Clouds could influence these chemical equilibria by changing the atmospheric temperature profile and/or through cloud particles acting as chemical catalysts.