Search Publications
Multifilter Observations of the Complex Periodic Variations in the M-dwarf Star RIK 90
Koen, Chris
The star RIK 90 is a member of a group of recently discovered young T Tauri stars showing complex periodic modulations of their light output, which have been difficult to explain. As one of the brightest, and having a relatively short period, RIK 90 is of particular interest. Thirty-three hours of contemporaneous BVRCIC photo…
The Hα line emission of the Be star β Psc: the last 40 yr
Diaz, Marcos P.; Amôres, Eduardo B.; Levenhagen, Ronaldo S. +1 more
A study on the photosphere and disc of the Be star β Psc is presented. We recover almost 40 yr of high-resolution spectroscopic observations and additional data gathered from the BeSS data base. We evaluate the photospheric parameters from the spectral energy distribution (SED) and fittings of state-of-the-art non-LTE model atmospheres to observed…
Searching for chemical abundance variations in young star clusters in the Magellanic Clouds: NGC 411, NGC 1718, and NGC 2213
Zucker, Daniel B.; de Grijs, Richard; Kapse, Shalmalee
The conventional picture of coeval, chemically homogeneous, populous star clusters - known as 'simple' stellar populations (SSPs) - is a view of the past. Photometric and spectroscopic studies reveal that almost all ancient globular clusters in the Milky Way and our neighbouring galaxies exhibit star-to-star light-element abundance variations, typ…
Effects of anisotropy on absorption cross-section spectra of medium-sized spheroidal corundum particles
Mutschke, H.; Höfer, S.; Mayerhöfer, Th. G.
Context. It has been widely accepted that corundum particles condense in the atmospheres of oxygen-rich asymptotic giant branch stars and effectively produce an infrared emission feature at 13 µm. Laboratory experiments have predicted that these particles have the shape of oblate spheroids.
Aims: We investigate the influence of the mate…
A search for pulsar companions around low-mass white dwarfs
Kramer, Michael; Athanasiadis, Tilemachos M.; Berezina, Marina +4 more
We report on a search for pulsars at the positions of eight low-mass white dwarfs and one higher mass white dwarf with the 100-m Effelsberg Radio Telescope. These systems have orbital parameters suggesting that their unseen companions are either massive white dwarfs or neutron stars (NSs). Our observations were performed at 1.36 GHz, reaching sens…
Blending and obscuration in weak-lensing magnification
Gaztanaga, E.; Schmidt, S. J.; Tyson, J. A. +1 more
We test the impact of some systematic errors in weak-lensing (WL) magnification measurements with the COSMOS 30-band photo-z Survey flux limited to Iauto < 25.0 using correlations of both source galaxy counts and magnitudes. Systematic obscuration effects are measured by comparing counts and magnification correlations. We use the Adv…
Ionic loss from Venus upper ionosphere via plasma wake
Moslem, W. M.; Elsheikh, I. A.; Tolba, R. E. +2 more
Recent observations have detected significant escape of ions from the Venusian ionosphere. The measurements indicate that the composition of the escaping mix of ions may reach a critical ratio of H+ : O+ ≈ 2 : 1 , suggesting that it originated in water molecules, in line with the observed dryness of the planet. In this work, …
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…
The ionization fraction in OMC-2 and OMC-3
Menten, K. M.; Tielens, A. G. G. M.; Wyrowski, F. +4 more
Context. The electron density (ne−) plays an important role in setting the chemistry and physics of the interstellar medium. However, measurements of ne− in neutral clouds have been directly obtained only toward a few lines of sight or they rely on indirect determinations.
Aims: We use carbon radio …
X-Rays in Cepheids: XMM-Newton Observations of η Aql
Mérand, Antoine; Drake, Jeremy J.; Guzik, Joyce A. +13 more
X-ray bursts have recently been discovered in the Cepheids δ Cep and β Dor modulated by the pulsation cycle. We have obtained an observation of the Cepheid η Aql with the XMM-Newton satellite at the phase of maximum radius; the phase at which there is a burst of X-rays in δ Cep. No X-rays were seen from the Cepheid η Aql at this phase, and the imp…