Search Publications
Thermophysical Characterization of Cyclic Frost Formation in the Subsurface and Nominal Water Activity on Comets: Case Study of 67P/Churyumov-Gerasimenko
Shi, Xian; Hu, Xuanyu
We use a generic thermophysical model to study in detail the formation of water-ice frost in the near-surface layers of comet 67P/Churyumov-Gerasimenko. We show that nightly frost formation is a common phenomenon. In particular, while abrupt landscapes may be conducive to frost formation, they are not a requisite condition. We show that the proces…
Sustaining Star Formation in the Galactic Star Cluster M 36?
Chen, Wen Ping; Gao, Yu; Sun, Yan +3 more
We present comprehensive characterization of the Galactic open cluster M 36. Some 200 member candidates, with an estimated contamination rate of ∼8%, have been identified on the basis of proper motion and parallax measured by the Gaia DR2. The cluster has a proper motion grouping around ( ${\mu }_{\alpha }\cos \delta =-0.15\pm 0.01$ <!-- -->…
Dynamics of Sunspot Shock Waves in the Chromosphere and Transition Region
Kayshap, Pradeep; Tripathi, Durgesh; Jelínek, P.
We study the dynamics of shock waves observed in the umbra of a sunspot using the spectroscopic observations from the Interface Region Imaging Spectrograph. The presence of a shock significantly deforms the shape of the spectral lines of Mg II, C II, and Si IV. We found that C II 1335.71 Å and Si IV 1393.75 Å show double-peaked profiles that chang…
Shocks and Molecules in Diffuse Interstellar Cloud Pairs
Heiles, Carl; Reach, William T.
The diffuse interstellar medium (ISM) is dynamic, and its chemistry and evolution are determined by shock fronts as well as photodissociation. Shocks are implied by the supersonic motions and velocity dispersion, often statistically called "turbulence". We compare models of magnetohydrodynamic (MHD) shocks, with speeds typical of cloud motions thr…
Physical Characteristics of Unstructured Coronal Clouds
Golub, L.; Hahn, M.; Savin, D. W. +2 more
Active regions in the inner solar corona, when observed in X-ray emission, consist of bright, hot loops surrounded by unstructured clouds. The emission from the clouds extends to a height of ≈4-5 × 104 km at temperatures of ≈2-3 MK. These "hot clouds" are variable, but persist for many days and do not appear to connect directly to the a…
Characterization of HD 206893 B from Near- to Thermal-infrared
Lee, Eve J.; Gao, Peter; Beichman, Charles +9 more
HD 206893 B is a brown-dwarf companion orbiting inside the debris disk of its host star. We detect the brown dwarf in the Ms band using the Keck/NIRC2 instrument and vortex coronagraph. We measure its magnitude to be ${Ms}={12.97}_{-0.11}^{0.10}$ . It is at an angular separation of 0"22 ± 0"03, and a position angle of 39.6° ± 5.4° east of north. U…
Limits to Ionization-parameter Mapping as a Diagnostic of HII Region Optical Depth
Oey, M. S.; Sawant, Amit N.; Micheva, Genoveva +2 more
We employ ionization-parameter mapping (IPM) to infer the optical depth of H II regions in the northern half of M33. We construct [O III]λ5007/[O II]λ3727 and [O III]λ5007/[S II]λ6724 ratio maps from narrowband images continuum-subtracted in this way, from which we classify the H II regions by optical depth to ionizing radiation, based on their io…
GTC/CanariCam Deep Mid-infrared Imaging Survey of Northern Stars within 5 pc
Rebolo, Rafael; Caballero, José A.; Pinfield, David J. +7 more
In this work we present the results of a direct imaging survey for brown dwarf companions around the nearest stars at the mid-infrared 10 micron range (λ c = 8.7 µm, Δλ = 1.1 µm) using the CanariCam instrument on the 10.4 m Gran Telescopio Canarias (GTC). We imaged the 25 nearest stellar systems within 5 pc of the Sun at d…
Blueshifted Hydrogen Emission and Shock Wave of RR Lyrae Variables in SDSS and LAMOST
Deng, Licai; Liu, Chao; Zhang, Huawei +4 more
Hydrogen emissions of RR Lyrae variables are the imprints of shock waves traveling through their atmospheres. We develop a pattern recognition algorithm, which is then applied to single-epoch spectra of the Sloan Digital Sky Survey and the Large Sky Area Multi-Object Fiber Spectroscopic Telescope survey. These two spectroscopic surveys covered ~10…
Multi-scale Radio and X-Ray Structure of the High-redshift Quasar PMN J0909+0354
Paragi, Zsolt; Frey, Sándor; Perger, Krisztina +3 more
The high-redshift quasar PMN J0909+0354 (z = 3.288) is known to have a parsec-scale compact jet structure, based on global 5 GHz very long baseline interferometry (VLBI) observations performed in 1992. Its kiloparsec-scale structure was studied with the Karl G. Jansky Very Large Array (VLA) in the radio and the Chandra space telescope in X-rays. A…