754 research outputs found
The Outer Envelopes of Globular Clusters. II. NGC 1851, NGC 5824 and NGC 1261
We present a second set of results from a wide-field photometric survey of
the environs of Milky Way globular clusters. The clusters studied are NGC 1261,
NGC 1851 and NGC 5824: all have data from DECam on the Blanco 4m telescope. NGC
5824 also has data from the Magellan Clay telescope with MegaCam. We confirm
the existence of a large diffuse stellar envelope surrounding NGC 1851 of size
at least 240 pc in radius. The radial density profile of the envelope follows a
power-law decline with index and the projected shape is
slightly elliptical. For NGC 5824 there is no strong detection of a diffuse
stellar envelope, but we find the cluster is remarkably extended and is similar
in size (at least 230 pc in radius) to the envelope of NGC 1851. A stellar
envelope is also revealed around NGC 1261. However, it is notably smaller in
size with radius 105 pc. The radial density profile of the envelope is
also much steeper with . We discuss the possible nature
of the diffuse stellar envelopes, but are unable to draw definitive conclusions
based on the current data. NGC 1851, and potentially NGC 5824, could be
stripped dwarf galaxy nuclei, akin to the cases of Cen, M54 and M2. On
the other hand, the different characteristics of the NGC 1261 envelope suggest
that it may be the product of dynamical evolution of the cluster.Comment: 18 pages, 11 figures, accepted to MNRA
Self-consistent propagation of flux ropes in realistic coronal simulations
The aim of this paper is to demonstrate the possible use of the new coronal
model COCONUT to compute a detailed representation of a numerical CME at
0.1~AU, after its injection at the solar surface and propagation in a realistic
solar wind, as derived from observed magnetograms. We present the
implementation and propagation of modified Titov-D\'emoulin (TDm) flux ropes in
the COCONUT 3D MHD coronal model. The background solar wind is reconstructed in
order to model two opposite configurations representing a solar activity
maximum and minimum respectively. Both were derived from magnetograms which
were obtained by the Helioseismic and Magnetic Imager (HMI) onboard the Solar
Dynamic Observatory (SDO) satellite. We track the propagation of 24 flux ropes,
which differ only by their initial magnetic flux. We especially investigate the
geometry of the flux rope during the early stages of the propagation as well as
the influence of its initial parameters and solar wind configuration on 1D
profiles derived at 0.1~AU. At the beginning of the propagation, the shape of
the flux ropes varies between simulations during low and high solar activity.
We find dynamics that are consistent with the standard CME model, such as the
pinching of the legs and the appearance of post-flare loops. Despite the
differences in geometry, the synthetic density and magnetic field time profiles
at 0.1~AU are very similar in both solar wind configurations. These profiles
are similar to those observed further in the heliosphere and suggest the
presence of a magnetic ejecta composed of the initially implemented flux rope
and a sheath ahead of it. Finally, we uncover relationships between the
properties of the magnetic ejecta, such as density or speed and the initial
magnetic flux of our flux ropes.Comment: 20 pages, 13 figure
Forward and Back: Kinematics of the Palomar 5 Tidal Tails
The tidal tails of Palomar 5 (Pal 5) have been the focus of many
spectroscopic studies in an attempt to identify individual stars lying along
the stream and characterise their kinematics. The well-studied trailing tail
has been explored out to a distance of 15^\text{o} from the cluster centre,
while less than four degrees have been examined along the leading tail. In this
paper, we present results of a spectroscopic study of two fields along the
leading tail that we have observed with the AAOmega spectrograph on the
Anglo-Australian telescope. One of these fields lies roughly 7^\text{o} along
the leading tail, beyond what has been previously been explored
spectroscopically. Combining our measurements of kinematics and line strengths
with Pan-STARRS1 photometric data and Gaia EDR3 astrometry, we adopt a
probabilistic approach to identify 16 stars with high probability of belonging
to the Pal 5 stream. Eight of these stars lie in the outermost field and their
sky positions confirm the presence of ``fanning'' in the leading arm. We also
revisit previously-published radial velocity studies and incorporate Gaia EDR3
astrometry to remove interloping field stars. With a final sample of 109 {\it
bona fide} Pal 5 cluster and tidal stream stars, we characterise the 3D
kinematics along the the full extent of the system. We provide this catalogue
for future modeling work.Comment: 13 pages, 8 figures, accepted for publication in MNRAS. The extended
version of Table 4 is available as an ancillery file, and will be
supplementary material in MNRA
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