Browsing by Author "Kurtev, Radostin"

Now showing 1 - 4 of 4
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    Candidate star clusters toward the inner Milky Way discovered on deep-stacked K-S-band images from the VVV Survey
    (2017) Ivanov, Valentin D.; Piatti, Andrés E,; Beamin Muhlenbrock, Juan Carlos; Minniti, D.; Borissova, Jordanka; Kurtev, Radostin; Hempel, Maren; Saito, Roberto K
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    RGB Properties of the LMC/SMC Clusters in the Infrared
    (2009) Kurtev, Radostin; Ivanov, Valentin; Borissova, Jura; Catelan , Marcio; Geisler, Douglas
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    The most variable VVV sources: eruptive protostars, dipping giants in the Nuclear Disc and others
    (2023) Lucas, Phil; Smith, Leigh; Guo, Zhen; Contreras Peña, Carlos; Minniti, Dante; Miller, Niall; Alonso-Garcia, Javier; Catelan, Marcio; Borissova, J.; Saito, Roberto; Kurtev, Radostin; Navarro, M. G.; Morris, Calum; Muthu, Hariharan; Froebrich, Dirk; Ivanov, Valentin; Bayo, Amelia; Caratti, Alessio; Sanders, Jason
    We have performed a comprehensive search of a VISTA Variables in the Via Lactea (VVV) data base of 9.5 yr light curves for variable sources with ΔKs ≥ 4 mag, aiming to provide a large sample of high amplitude eruptive young stellar objects (YSOs) and detect unusual or new types of infrared variable source. We find 222 variable or transient sources in the Galactic bulge and disc, most of which are new discoveries. The sample mainly comprises novae, YSOs, microlensing events, Long Period Variable stars (LPVs), and a few rare or unclassified sources. Additionally, we report the discovery of a significant population of aperiodic late-type giant stars suffering deep extinction events, strongly clustered in the Nuclear Disc of the Milky Way. We suggest that these are metal-rich stars in which radiatively driven mass loss has been enhanced by super-solar metallicity. Among the YSOs, 32/40 appear to be undergoing episodic accretion. Long-lasting YSO eruptions have a typical rise time of ∼2 yr, somewhat slower than the 6–12 month time-scale seen in the few historical events observed on the rise. The outburst durations are usually at least 5 yr, somewhat longer than many lower amplitude VVV events detected previously. The light curves are diverse in nature, suggesting that multiple types of disc instability may occur. Eight long-duration extinction events are seen wherein the YSO dims for a year or more, attributable to inner disc structure. One binary YSO in NGC 6530 displays periodic extinction events (P=59 d) similar to KH 15D.
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    Variable stars in the Galactic center, as revealed by the VVV Survey
    (2017) Molina, Claudio Navarro; Borissova, Jura; Catelan, Márcio; Kurtev, Radostin; Medina, Nicolás
    A variability search has been performed in the Galactic center, using the nearinfrared images from the Vista Variables in the Vía Láctea (VVV) Survey. Light curves contain 89 epochs in the KS band. A total of 353 variable stars were found, of which only 47 are already present in the literature.