Search Publications
The vertical force in the solar neighbourhood using red clump stars in TGAS and RAVE. Constraints on the local dark matter density
Helmi, Amina; Hagen, Jorrit H. J.
Aims: We investigate the kinematics of red clump (RC) stars in the solar neighbourhood by combining data from Tycho-Gaia Astrometric Solution (TGAS) and Radial Velocity Experiment (RAVE) to constrain the local dark matter density.
Methods: After calibrating the absolute magnitude of RC stars, we characterized their velocity distribution …
A closer look at the transition between fully convective and partly radiative low-mass stars
Baraffe, Isabelle; Chabrier, Gilles
Recently, an analysis of Gaia Data Release 2 revealed a gap in the mid-M dwarf main sequence. The authors suggested the feature is linked to the onset of full convection in M dwarfs. Following the announcement of this discovery, an explanation has been proposed based on standard stellar evolution models. In this paper we re-examine this explanatio…
The XXL Survey. XVI. The clustering of X-ray selected galaxy clusters at z 0.3
Altieri, B.; Valtchanov, I.; Lidman, C. +20 more
Context. Galaxy clusters trace the highest density peaks in the large-scale structure of the Universe. Their clustering provides a powerful probe that can be exploited in combination with cluster mass measurements to strengthen the cosmological constraints provided by cluster number counts.
Aims: We investigate the spatial properties of a hom…
Extreme submillimetre starburst galaxies
Rowan-Robinson, M.; Clements, David L.; Pearson, William J. +6 more
We have used two catalogues, a Herschel catalogue selected at 500 µm (HerMES) and an IRAS catalogue selected at 60 µm (RIFSCz), to contrast the sky at these two wavelengths. Both surveys demonstrate the existence of "extreme" starbursts, with star-formation rates (SFRs) > 5000 M⊙ yr-1. The maximum intrinsic sta…
The dynamically selected stellar halo of the Galaxy with Gaia and the tilt of the velocity ellipsoid
Helmi, Amina; Veljanoski, Jovan; Breddels, Maarten A. +1 more
Aims: We study the dynamical properties of halo stars located in the solar neighbourhood. Our goal is to explore how the properties of the halo depend on the selection criteria used to define a sample of halo stars. Once this is understood, we proceed to measure the shape and orientation of the halo's velocity ellipsoid and we use this inform…
The MUSE Hubble Ultra Deep Field Survey. XII. Mg II emission and absorption in star-forming galaxies
Feltre, Anna; Bacon, Roland; Tresse, Laurence +18 more
The physical origin of the near-ultraviolet Mg II emission remains an underexplored domain, unlike more typical emission lines that are detected in the spectra of star-forming galaxies. We explore the nebular and physical properties of a sample of 381 galaxies between 0.70 < z < 2.34 drawn from the MUSE Hubble Ultra Deep Survey. The spectra …
The magnetic nature of umbra-penumbra boundary in sunspots
Jurčák, J.; Schlichenmaier, R.; Rezaei, R. +2 more
Context. Sunspots are the longest-known manifestation of solar activity, and their magnetic nature has been known for more than a century. Despite this, the boundary between umbrae and penumbrae, the two fundamental sunspot regions, has hitherto been solely defined by an intensity threshold. Aim. Here, we aim at studying the magnetic nature of umb…
The Gaia-ESO Survey: a kinematical and dynamical study of four young open clusters
Gilmore, G.; Bayo, A.; Koposov, S. E. +32 more
Context. The origin and dynamical evolution of star clusters is an important topic in stellar astrophysics. Several models have been proposed in order to understand the formation of bound and unbound clusters and their evolution, and they can be tested by examining the kinematical and dynamical properties of clusters over a wide range of ages and …
X-shooter observations of low-mass stars in the η Chamaeleontis association
Herczeg, Gregory; Fedele, Davide; Rugel, Michael
The nearby η Chamaeleontis association is a collection of 4-10 Myr old stars with a disk fraction of 35-45%. In this study, the broad wavelength coverage of VLT/X-shooter is used to measure the stellar and mass accretion properties of 15 low-mass stars in the η Chamaeleontis association. For each star, the observed spectrum is fitted with a non-ac…
The Gaia-ESO Survey: Lithium enrichment histories of the Galactic thick and thin disc
Bayo, A.; Lardo, C.; Randich, S. +32 more
Lithium abundance in most of the warm metal-poor main sequence stars shows a constarnt plateau (A(Li) 2.2 dex) and then the upper envelope of the lithium vs. metallicity distribution increases as we approach solar metallicity. Meteorites, which carry information about the chemical composition of the interstellar medium (ISM) at the solar system fo…