11,591 research outputs found
EPIC247098361b: a transiting warm Saturn on an eccentric days orbit around a star
We report the discovery of EPIC247098361b using photometric data of the
Kepler K2 satellite coupled with ground-based spectroscopic observations.
EPIC247098361b has a mass of M M, a radius of
R R, and a moderately low equilibrium temperature of
K due to its relatively large star-planet separation of
AU. EPIC247098361b orbits its bright () late F-type host star
in an eccentric orbit () every 11.2 days, and is one of only
four well characterized warm Jupiters having hosts stars brighter than .
We estimate a heavy element content of 20 7 M for
EPIC247098361b, which is consistent with standard models of giant planet
formation. The bright host star of EPIC247098361b makes this system a well
suited target for detailed follow-up observations that will aid in the study of
the atmospheres and orbital evolution of giant planets at moderate separations
from their host stars.Comment: 11 pages, 10 figures, submitted to MNRA
The Nature of UCDs: Internal Dynamics from an Expanded Sample and Homogeneous Database
We have obtained high-resolution spectra of 23 ultra-compact dwarf galaxies
(UCDs) in the Fornax cluster with -10.4>M_V>-13.5 mag (10^6<M/M_*<10^8), using
FLAMES/Giraffe at the VLT. This is the largest homogeneous data set of UCD
internal dynamics assembled to date. We derive dynamical M/L ratios for 15 UCDs
covered by HST imaging. In the M_V-sigma plane, UCDs with M_V<-12 mag are
consistent with the extrapolated Faber-Jackson relation for luminous
ellipticals, while fainter UCDs are closer to the extrapolated globular cluster
(GC) relation. At a given metallicity, Fornax UCDs have on average 30-40% lower
M/L ratios than Virgo UCDs, suggesting possible differences in age or dark
matter content between Fornax and Virgo UCDs. For our sample of Fornax UCDs we
find no significant correlation between M/L ratio and mass. We combine our data
with available M/L ratio measurements of compact stellar systems with
10^4<M/M_*<10^8, and normalise all M/L estimates to solar metallicity. We find
that UCDs (M > 2*10^6 M_*) have M/L ratios twice as large as GCs (M < 2*10^6
M_*). We show that stellar population models tend to under-predict dynamical
M/L ratios of UCDs and over-predict those of GCs. Considering the scaling
relations of stellar spheroids, UCDs align well along the 'Fundamental
Manifold', constituting the small-scale end of the galaxy sequence. The
alignment for UCDs is especially clear for r_e >~ 7 pc, which corresponds to
dynamical relaxation times that exceed a Hubble time. In contrast, GCs exhibit
a broader scatter and do not appear to align along the manifold. We argue that
UCDs are the smallest dynamically un-relaxed stellar systems, with M > 2*10^6
M_* and 7<r_e<100 pc. Future studies should aim at explaining the elevated M/L
ratios of UCDs and the environmental dependence of their properties.Comment: 17 pages, 14 figures, accepted for publication in A&A. V3 taking into
account proof corrections: Table 3 radial velocity entries corrected by
heliocentric correction, updated sigma entries in Table 5 for a few CenA
sources, updated references for G1 and omega Ce
Clustering of Local Group distances: publication bias or correlated measurements? VII. A distance framework out to 100 Mpc
We consider the published distance moduli to the Fornax and Coma galaxy
clusters, with emphasis on the period since 1990. We have carefully homogenized
our catalogs of distance moduli onto the distance scale established in the
previous papers in this series. We assessed systematic differences associated
with the use of specific tracers, and discarded results based on application of
the Tully--Fisher relation and of globular cluster and planetary nebula
luminosity functions. We recommend `best' weighted relative distance moduli for
the Fornax and Coma clusters with respect to the Virgo cluster of mag and mag. The set of weighted mean distance moduli
(distances) we derived as most representative of the clusters' distances is,
\begin{eqnarray} (m-M)_0^{\rm Fornax} &=& 31.41 \pm 0.15 \mbox{ mag } (D =
19.1^{+1.4}_{-1.2} \mbox{ Mpc) and} \nonumber
&=& 31.21 \pm 0.28 \mbox{ mag } (D = 17.5^{+2.4}_{-2.2} \mbox{ Mpc)};
\nonumber \\ (m-M)_0^{\rm Coma} &=& 34.99 \pm 0.38 \mbox{ mag } (D =
99.5^{+19.0}_{-15.9} \mbox{ Mpc) and} \nonumber
&=& 34.78 \pm 0.27 \mbox{ mag } (D = 90.4^{+11.9}_{-10.6} \mbox{ Mpc)},
\nonumber \end{eqnarray} where the first value for each cluster is the result
of our analysis of the direct distance moduli, while the second modulus is
based on distance moduli relative to the Virgo cluster. The absolute and
relative distance moduli for both clusters are mutually consistent within the
uncertainties; the relative distance moduli yield shorter distances by
1. Lingering uncertainties in the underlying absolute distance
scale appear to have given rise to a systematic uncertainty on the order of
0.20 mag.Comment: 15 pages, 3 figures; accepted for publication in ApJ
A discontinuity in the -radius relation of M-dwarfs
We report on 13 new high-precision measurements of stellar diameters for
low-mass dwarfs obtained by means of near-infrared long-baseline interferometry
with PIONIER at the Very Large Telescope Interferometer. Together with accurate
parallaxes from Gaia DR2, these measurements provide precise estimates for
their linear radii, effective temperatures, masses, and luminosities. This
allows us to refine the effective temperature scale, in particular towards the
coolest M-dwarfs. We measure for late-type stars with enhanced metallicity
slightly inflated radii, whereas for stars with decreased metallicity we
measure smaller radii. We further show that Gaia DR2 effective temperatures for
M-dwarfs are underestimated by 8.2 % and give an empirical
- relation which is better suited for M-dwarfs with between 2600 and 4000 K. Most importantly, we are able to observationally
identify a discontinuity in the -radius plane, which is likely due
to the transition from partially convective M-dwarfs to the fully convective
regime. We found this transition to happen between 3200 K and 3340 K, or
equivalently for stars with masses . We find that in
this transition region the stellar radii are in the range from 0.18 to
0.42 for similar stellar effective temperatures.Comment: 11 pages, 9 figures, accepted in MNRA
HATS-11b and HATS-12b: Two transiting Hot Jupiters orbiting sub-solar metallicity stars selected for the K2 Campaign 7
We report the discovery of two transiting extrasolar planets from the
HATSouth survey. HATS-11, a V=14.1 G0-star shows a periodic 12.9 mmag dip in
its light curve every 3.6192 days and a radial velocity variation consistent
with a Keplerian orbit. HATS-11 has a mass of 1.000 0.060 M, a
radius of 1.444 0.057 M and an effective temperature of 6060
150 K, while its companion is a 0.85 0.12 M, 1.510 0.078
R planet in a circular orbit. HATS-12 shows a periodic 5.1 mmag flux
decrease every 3.1428 days and Keplerian RV variations around a V=12.8 F-star.
HATS-12 has a mass of 1.489 0.071 M, a radius of 2.21
0.21 R, and an effective temperature of 6408 75 K. For HATS-12,
our measurements indicate that this is a 2.38 0.11 M, 1.35 0.17
R planet in a circular orbit. Both host stars show sub-solar metallicity of
-0.390 0.060 dex and -0.100 0.040 dex, respectively and are
(slightly) evolved stars. In fact, HATS-11 is amongst the most metal-poor and,
HATS-12 is amongst the most evolved stars hosting a hot Jupiter planet.
Importantly, HATS-11 and HATS-12 have been observed in long cadence by Kepler
as part of K2 campaign 7 (EPIC216414930 and EPIC218131080 respectively).Comment: 14 pages, 7 figures, 6 tables, submitted to A
The Future of Direct Supermassive Black Hole Mass Estimates
(Abridged) The repeated discovery of supermassive black holes (SMBHs) at the
centers of galactic bulges, and the discovery of relations between the SMBH
mass (M) and the properties of these bulges, has been fundamental in directing
our understanding of both galaxy and SMBH formation and evolution. However,
there are still many questions surrounding the SMBH - galaxy relations. For
example, are the scaling relations linear and constant throughout cosmic
history, and do all SMBHs lie on the scaling relations? These questions can
only be answered by further high quality direct M estimates from a wide range
in redshift. In this paper we determine the observational requirements
necessary to directly determine SMBH masses, across cosmological distances,
using current M modeling techniques. We also discuss the SMBH detection
abilities of future facilities. We find that if different M modeling
techniques, using different spectral features, can be shown to be consistent,
then both 30 m ground- and 16 m space-based telescopes will be able to sample M
1e9Msol across ~95% of cosmic history. However, we find that the abilities of
ground-based telescopes critically depend on future advancements in adaptive
optics systems; more limited AO systems will result in limited effective
spatial resolutions, and forces observations towards the near-infrared where
spectral features are weaker and more susceptible to sky features. Ground-based
AO systems will always be constrained by relatively bright sky backgrounds and
atmospheric transmission. The latter forces the use of multiple spectral
features and dramatically impacts the SMBH detection efficiency. The most
efficient way to advance our database of direct SMBH masses is therefore
through the use of a large (16 m) space-based UVOIR telescope.Comment: PASP Accepte
HST hot-Jupiter transmission spectral survey: Haze in the atmosphere of WASP-6b
We report Hubble Space Telescope (HST) optical to near-infrared transmission
spectroscopy of the hot Jupiter WASP-6b, measured with the Space Telescope
Imaging Spectrograph (STIS) and Spitzer's InfraRed Array Camera (IRAC). The
resulting spectrum covers the range m. We find evidence for
modest stellar activity of WASP-6b and take it into account in the transmission
spectrum. The overall main characteristic of the spectrum is an increasing
radius as a function of decreasing wavelength corresponding to a change of
from 0.33 to m. The spectrum suggests
an effective extinction cross-section with a power law of index consistent with
Rayleigh scattering, with temperatures of K at the planetary
terminator. We compare the transmission spectrum with hot-Jupiter atmospheric
models including condensate-free and aerosol-dominated models incorporating Mie
theory. While none of the clear-atmosphere models is found to be in good
agreement with the data, we find that the complete spectrum can be described by
models that include significant opacity from aerosols including Fe-poor
MgSiO, MgSiO, KCl and NaS dust condensates. WASP-6b is the
second planet after HD189733b which has equilibrium temperatures near
K and shows prominent atmospheric scattering in the optical.Comment: 18 pages, 15 figures, 7 table
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