A5049998079- Stellar, planetary, and galactic studies
- Astrophysics and Star Formation Studies
- Astronomy and Astrophysical Research
- Astro and Planetary Science
- Astronomical Observations and Instrumentation
- Astrophysical Phenomena and Observations
- Gamma-ray bursts and supernovae
- Atmospheric Ozone and Climate
- Phase Equilibria and Thermodynamics
- Spectroscopy and Laser Applications
- Adaptive optics and wavefront sensing
- Molecular Spectroscopy and Structure
- Solar and Space Plasma Dynamics
- Geophysics and Gravity Measurements
- Seismology and Earthquake Studies
- Calibration and Measurement Techniques
- Seismic Imaging and Inversion Techniques
- Magnetic Properties and Applications
- Ionosphere and magnetosphere dynamics
- Scientific Research and Discoveries
- Optical properties and cooling technologies in crystalline materials
- Space Exploration and Technology
- Cosmology and Gravitation Theories
- SAS software applications and methods
- Astrophysics and Cosmic Phenomena
Seoul National University
2022-2025
University of Hertfordshire
2013-2024
University of Exeter
2017-2022
Kyung Hee University
2022
Pontificia Universidad Católica de Chile
2013-2018
Aarhus University
2013-2018
Institute of Astrophysics and Space Sciences
2016
Universidade do Porto
2016
Universidad Andrés Bello
2015-2016
Millennium Institute of Astrophysics
2015-2016
We present VIRAC version 1, a near-infrared proper motion and parallax catalogue of the VISTA VVV survey for 312,587,642 unique sources averaged across all overlapping pawprint tile images covering 560 deg$^2$ bulge Milky Way southern disk. The includes 119 million high quality measurements, which 47 have statistical uncertainties below 1 mas yr$^{-1}$. In 11$<K_s<$14 magnitude range motions median uncertainty 0.67 also 6,935 with quality-controlled 5 $\sigma$ parallaxes 1.1 mas. show...
Abstract Variability in young stellar objects (YSOs) can be caused by various time-dependent phenomena associated with star formation, including accretion rates, geometric changes the circumstellar disks, stochastic hydromagnetic interactions between surfaces and inner-disk edges, reconnections within magnetosphere, hot/cold spots on surfaces. We uncover characterize ∼1700 variables from a sample of ∼5400 YSOs nearby low-mass star-forming regions using mid-IR light curves obtained 6.5 yr...
ABSTRACT During the pre-main-sequence (pre-MS) evolution stage of a star, significant amounts stellar mass are accreted during episodic accretion events, such as multidecade FUor-type outbursts. Here, we present near-infrared spectroscopic follow-up study 33 high-amplitude (most with ΔKs &gt; 4 mag) variable sources discovered by Vista Variables in Via Lactea (VVV) survey. Based on spectral features, 25 classified eruptive young objects (YSOs), including 15 newly identified FUors, six...
We present the discovery of 816 high amplitude infrared variable stars ($\Delta K_{\rm s} >$ 1 mag) in 119 deg$^2$ Galactic midplane covered by Vista Variables Via Lactea (VVV) survey. Almost all are new discoveries and about 50$\%$ YSOs. This provides further evidence that YSOs commonest plane. In 2010-2014 time series likely we find variability increases towards younger evolutionary classes (class I flat-spectrum sources) except on short timescales ($<$25 days) where this trend is...
In a companion work (Paper I) we detected large population of highly variable Young Stellar Objects (YSOs) in the Vista Variables Via Lactea (VVV) survey, typically with class I or flat spectrum spectral energy distributions and diverse light curve types. Here present infrared spectra (0.9--2.5 $\mu$m) 37 these variables, many them observed bright state. The confirm that 15/18 sources eruptive curves have signatures high accretion rate, either showing EXor-like emission features ($\Delta$v=2...
Abstract We report on the source Gaia 17bpi and identify it as a new, ongoing FU Ori–type outburst, associated with young stellar object. The optical light curve from exhibited 3.5 mag rise appearing to plateau in mid-/late 2018. Mid-infrared observations NEOWISE also show >3 that occurred two stages, second one coincident brightening, first preceding brightening by ∼1.5 yr. model outburst having started between October December of 2014. This wavelength-dependent aspect star...
Abstract The James Clerk Maxwell Telescope (JCMT) Transient Survey has been monitoring eight Gould Belt low-mass star-forming regions since 2015 December and six somewhat more distant intermediate-mass 2020 February with the Submillimeter Common User Bolometer Array 2 on board JCMT at 450 850 μ m an approximately monthly cadence. We introduce our pipeline v2 relative calibration procedures for image alignment flux across epochs, improving previous v1 by decreasing measurement uncertainties...
We have determined the rate of large accretion events in class I and II young stellar objects (YSOs) by comparing all-sky digitised photographic plate surveys provided SuperCOSMOS with latest data release from Gaia (DR2). The long mean baseline 55 years along a sample YSOs ($\simeq$15,000) allows us to study approximately 1 million YSO-years. find 139 $ΔR\geq1$~mag, most which are found at amplitudes between 3 mag. majority this group show irregular variability or long-lasting fading events,...
Abstract We present the four-year survey results of monthly submillimeter monitoring eight nearby (<500 pc) star-forming regions by JCMT Transient Survey. apply Lomb–Scargle Periodogram technique to search for and characterize variability on 295 peaks brighter than 0.14 Jy beam −1 , including 22 disk sources (Class II), 83 protostars 0/I), 190 starless sources. uncover 18 secular variables, all them protostars. No single-epoch burst or drop events no inherently stochastic are observed....
ABSTRACT Episodic accretion is one of the competing models to explain observed luminosity spread in young stellar clusters. These short-lived high events could also have a strong impact on planet formation. Observations high-amplitude variability objects (YSOs) due large changes rate provide direct observational evidence for episodic accretion. However, there are still uncertainties frequency these and if universal among YSOs. To determine outbursts Class I YSOs, we built robust sample at...
We have performed a comprehensive search of VISTA Variables in the Via Lactea (VVV) database 9.5 yr light curves for variable sources with $\Delta K_s \ge 4$ mag, aiming to provide large sample high amplitude eruptive young stellar objects (YSOs) and detect unusual or new types infrared source. find 222 transient Galactic bulge disc, most which are discoveries. The mainly comprises novae, YSOs, microlensing events, Long Period Variable stars (LPVs) few rare unclassified sources....
Context. The ESO public survey VISTA Variables in the Vía Láctea (VVV) surveyed inner Galactic bulge and adjacent southern disk from 2009–2015. Upon its conclusion, complementary VVV extended (VVVX) has expanded both temporal as well spatial coverage of original area, widening it 562 to 1700 sq. deg., providing additional epochs JHK s filters 2016–2023. Aims. With completion VVVX observations during first semester 2023, we present here observing strategy, a description data quality access,...
Abstract FU Ori-type objects (FUors) are decades-long outbursts of accretion onto young stars that strong enough to viscously heat disks so the disk outshines central star. We construct models for FUor by calculating emission components from a steady-state viscous disk, passively-heated dusty magnetospheric columns, and stellar photosphere. explore parameter space rate <?CDATA $\dot{M}$?> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true">...
Abstract Protostellar outflows often present a knotty appearance, providing evidence of sporadic accretion in stellar mass growth. To understand the direct relation between and ejection, we analyze contemporaneous activity associated ejection components B335. B335 has brightened mid-IR by 2.5 mag since 2010, indicating increased luminosity, presumably due to an rate onto protostar. Atacama Large Millimeter/submillimeter Array (ALMA) observations 12 CO emission outflow reveal high-velocity...
We study the relationship between mid-infrared and sub-mm variability of deeply embedded protostars using multi-epoch data from Wide Infrared Survey Explorer ($WISE$/NEOWISE) ongoing James Clerk Maxwell Telescope (JCMT) transient survey. Our search for signs stochastic (random) and/or secular (roughly monotonic in time) a sample 59 young stellar objects (YSOs) revealed that 35 are variable at least one two surveys. This is dominated by changes. Of those with variability, 14 ($22\%$ sample)...
While young stellar objects sometimes undergo bursts of accretion, these usually occur sporadically, making them challenging to study observationally and explain theoretically. We build a schematic description cyclical the object EC 53 using near-IR sub-mm monitoring obtained over six cycles, each lasting $\approx530$ days. brightens $0.12$ yr by $0.3$ mag at 850 $\mu$m, $2$ 3.35 $1.5$ wavelengths, maximum luminosity consistent with an accretion rate $\sim8\times10^{-6}$ M$_\odot$ yr$^{-1}$....
ABSTRACT The decade-long Vista Variables in the Via Lactea (VVV) survey has detected numerous highly variable young stellar objects (YSOs). We present a study of 61 VVV YSOs (ΔKs = 1–5 mag), combining near-infrared spectra from Magellan and ESO Very Large Telescope with NEOWISE light curves to investigate physical mechanisms behind eruptive events. Most sources are spectroscopically confirmed as variables (typically Class I YSOs) but extinction is also seen. Among them, magnetically...
Observed changes in protostellar brightness can be complicated to interpret. In our JCMT~Transient monitoring survey, we discovered that a young binary protostar, HOPS 373, is undergoing modest $30\%$ increase at 850 $\mu$m, caused by factor of 1.8$-$3.3 enhancement the accretion rate. The initial burst occurred over few months, with sharp rise and then shallower decay. A second soon after decay, source still bright one year later. mid-IR emission, small-scale CO outflow mapped ALMA,...
The mass accretion process controls pre-main-sequence evolution, although its intrinsic instability has yet to be fully understood, especially towards the protostellar stage. In this work, we have undertaken a thorough examination of mid-infrared variability Spitzer-selected YSOs in Cygnus-X star-forming region over last decade, using NEOWISE time series. This work compares two groups young stars: embedded Class I objects, and more evolved flat-spectrum/Class II sources. We report on 48...
Abstract The mass accretion process controls pre-main-sequence evolution, although its intrinsic instability has yet to be fully understood, especially towards the protostellar stage. In this work, we have undertaken a thorough examination of mid-infrared variability Spitzer-selected YSOs in Cygnus-X star-forming region over last decade, using NEOWISE time series. This work compares two groups young stars: embedded Class I objects, and more evolved flat-spectrum/Class II sources. We report...
Abstract The James Clerk Maxwell Telescope (JCMT) Transient Survey recently discovered that the Class 0 protostar HOPS 358 decreased in 350 GHz continuum brightness by ∼25% over course of 4 yr before brightening again for next 4. JCMT light curve can be fit a long-timescale dip lasting roughly 8 yr. A shorter-timescale periodicity is also apparent with period 1.75 and small 3% amplitude. NEOWISE monitoring reveals mid-infrared wavelength follows similar long-term pattern time. Here, we...
Context. The Vista Variables in the Vía Láctea (VVV) ESO Public Survey is a variability survey of Milky Way bulge and an adjacent section disk carried out from 2010 on Visible Infrared Telescope for Astronomy (VISTA). VVV will eventually deliver deep near-IR atlas with photometry positions five passbands (ZYJHKS) catalogue 1−10 million variable point sources – mostly unknown that require classifications.
We present a catalogue of 618 high amplitude infrared variable stars (1 < DeltaK 5 mag) detected by the two widely separated epochs 2.2 um data in UKIDSS Galactic plane survey, from searches covering 1470 deg^2. Most were discovered search all fields at 30 l 230 deg. Sources include new dusty Mira variables, three CV candidates, blazar and peculiar source that may be an interacting binary system. However, c. 60 per cent are YSOs, based on spatial association with star forming regions...
Numerous eruptive variable young stellar objects (YSOs), mostly Class I systems, were recently detected by the near-infrared Vista Variables in Via Lactea (VVV) survey. We present an exploratory spectroscopic variability study of 14 YSOs. The variations sampled over 1-day and 1 to 2-year intervals analysed combination with VVV light curves. CO overtone absorption features are observed on 3 FUor-like spectra: all show deeper when they brighter. This implies stronger emission from...