19 research outputs found
Radial-velocity jitter of stars as a function of observational timescale and stellar age
Stars show various amounts of radial velocity (RV) jitter due to varying
stellar activity levels. The typical amount of RV jitter as a function of
stellar age and observational timescale has not yet been systematically
quantified, although it is often larger than the instrumental precision of
modern high-resolution spectrographs used for Doppler planet detection and
characterization. We aim to empirically determine the intrinsic stellar RV
variation for mostly G and K dwarf stars on different timescales and for
different stellar ages independently of stellar models. We also focus on young
stars ( 30 Myr), where the RV variation is known to be large. We use
archival FEROS and HARPS RV data of stars which were observed at least 30 times
spread over at least two years. We then apply the pooled variance (PV)
technique to these data sets to identify the periods and amplitudes of
underlying, quasiperiodic signals. We show that the PV is a powerful tool to
identify quasiperiodic signals in highly irregularly sampled data sets. We
derive activity-lag functions for 20 putative single stars, where lag is the
timescale on which the stellar jitter is measured. Since the ages of all stars
are known, we also use this to formulate an activity--age--lag relation which
can be used to predict the expected RV jitter of a star given its age and the
timescale to be probed. The maximum RV jitter on timescales of decades
decreases from over 500 m/s for 5 Myr-old stars to 2.3 m/s for stars with ages
of around 5 Gyr. The decrease in RV jitter when considering a timescale of only
1 d instead of 1 yr is smaller by roughly a factor of 4 for 5 Myr old stars,
and a factor of 1.5 for stars with an age of 5 Gyr. The rate at which the RV
jitter increases with lag strongly depends on stellar age and ranges from a few
days for a few 10 Myr old stars to presumably decades for stars with an age of
a few gigayears.Comment: 15 pages, 7 Figures; Changelog v2: Updated link to CDS for table E.1;
rearranged Fig. 2 to match journal layou
New HARPS and FEROS observations of GJ1046
In this paper we present new precise Doppler data of GJ1046 taken between
November 2005 and July 2018 with the HARPS and the FEROS high-resolution
spectographs. In addition, we provide a new stellar mass estimate of GJ1046 and
we update the orbital parameters of the GJ1046 system. These new data and
analysis could be used together with the GAIA epoch astrometry, when available,
for braking the degeneracy and revealing the true mass of the GJ1046
system.Comment: 2 pages, 1 figure, 1 table with RV data (available only in the
Astro-PH version of the paper), Accepted by RNAA
The LEECH Exoplanet Imaging Survey: Limits on Planet Occurrence Rates Under Conservative Assumptions
We present the results of the largest (m) direct
imaging survey for exoplanets to date, the Large Binocular Telescope
Interferometer (LBTI) Exozodi Exoplanet Common Hunt (LEECH). We observed 98
stars with spectral types from B to M. Cool planets emit a larger share of
their flux in compared to shorter wavelengths, affording LEECH an
advantage in detecting low-mass, old, and cold-start giant planets. We
emphasize proximity over youth in our target selection, probing physical
separations smaller than other direct imaging surveys. For FGK stars, LEECH
outperforms many previous studies, placing tighter constraints on the hot-start
planet occurrence frequency interior to au. For less luminous,
cold-start planets, LEECH provides the best constraints on giant-planet
frequency interior to au around FGK stars. Direct imaging survey
results depend sensitively on both the choice of evolutionary model (e.g., hot-
or cold-start) and assumptions (explicit or implicit) about the shape of the
underlying planet distribution, in particular its radial extent. Artificially
low limits on the planet occurrence frequency can be derived when the shape of
the planet distribution is assumed to extend to very large separations, well
beyond typical protoplanetary dust-disk radii ( au), and when
hot-start models are used exclusively. We place a conservative upper limit on
the planet occurrence frequency using cold-start models and planetary
population distributions that do not extend beyond typical protoplanetary
dust-disk radii. We find that of FGK systems can host a 7 to 10
planet from 5 to 50 au. This limit leaves open the
possibility that planets in this range are common.Comment: 31 pages, 13 figures, accepted to A
The transiting multi-planet system HD3167: a 5.7 MEarth Super-Earth and a 8.3 MEarth mini-Neptune
HD3167 is a bright (V=8.9 mag) K0V star observed by the NASA's K2 space
mission during its Campaign 8. It has been recently found to host two small
transiting planets, namely, HD3167b, an ultra short period (0.96 d)
super-Earth, and HD3167c, a mini-Neptune on a relatively long-period orbit
(29.85 d). Here we present an intensive radial velocity follow-up of HD3167
performed with the FIES@NOT, [email protected], and HARPS-N@TNG spectrographs. We
revise the system parameters and determine radii, masses, and densities of the
two transiting planets by combining the K2 photometry with our spectroscopic
data. With a mass of 5.69+/-0.44 MEarth, radius of 1.574+/-0.054 REarth, and
mean density of 8.00(+1.0)(-0.98) g/cm^3, HD3167b joins the small group of
ultra-short period planets known to have a rocky terrestrial composition.
HD3167c has a mass of 8.33 (+1.79)(-1.85) MEarth and a radius of
2.740(+0.106)(-0.100) REarth, yielding a mean density of 2.21(+0.56)(-0.53)
g/cm^3, indicative of a planet with a composition comprising a solid core
surrounded by a thick atmospheric envelope. The rather large pressure scale
height (about 350 km) and the brightness of the host star make HD3167c an ideal
target for atmospheric characterization via transmission spectroscopy across a
broad range of wavelengths. We found evidence of additional signals in the
radial velocity measurements but the currently available data set does not
allow us to draw any firm conclusion on the origin of the observed variation.Comment: 18 pages, 11 figures, 5 table
The transiting multi-planet system HD3167: a 5.7 MEarth Super-Earth and a 8.3 MEarth mini-Neptune
The prognostic value of SUMO1/Sentrin specific peptidase 1 (SENP1) in prostate cancer is limited to ERG-fusion positive tumors lacking PTEN deletion
Importance of Bubble Size Control in Ultrasonic Surface Cleaning by Pulsed High-Frequency Sound Fields
The occurrence of acoustic cavitation is incorporating a multitude of interdependent effects that strongly depend on the bubble size. Therefore, bubble size control would be beneficial for industrial processes that rely on acoustic cavitation. A pulsed acoustic field can result in bubble size control and bubble recycling, which strongly enhances cavitation activity. In this paper, we present experimentally determined bubble size distributions for different power densities, which are interpreted in the frame of numerical calculations of the oscillatory responses of the bubbles to the intermittent driving sound field. The distributions are found to be shaped by the size dependent interplay between bubble pulsations, rectified diffusion, coalescence and the development of parametrically amplified shape instabilities. Furthermore, a relation between cleaning and acoustic cavitation activity is established. The results show that the changed acoustic conditions bubbles experience in close vicinity to a solid surface, need to be taken into account. The influence of the inertial type of cavitation activity on the structural damage that is occurring during the cleaning process, is evaluated. It is found that the damage to the fragile structures that ought to be cleaned, is significantly reduced, when the applied power is kept below values, for which inertial cavitation is observed. © 2013 The Electrochemical Society. All rights reserved.status: publishe
Towards an understanding and control of cavitation activity in 1 MHz ultrasound fields
Various industrial processes such as sonochemical processing and ultrasonic cleaning strongly rely on the
phenomenon of acoustic cavitation. As the occurrence of acoustic cavitation is incorporating a multitude
of interdependent effects, the amount of cavitation activity in a vessel is strongly depending on the ultrasonic
process conditions. It is therefore crucial to quantify cavitation activity as a function of the process
parameters. At 1 MHz, the active cavitation bubbles are so small that it is becoming difficult to observe
them in a direct way. Hence, another metrology based on secondary effects of acoustic cavitation is more
suitable to study cavitation activity. In this paper we present a detailed analysis of acoustic cavitation
phenomena at 1 MHz ultrasound by means of time-resolved measurements of sonoluminescence, cavitation
noise, and synchronized high-speed stroboscopic Schlieren imaging. It is shown that a correlation
exists between sonoluminescence, and the ultraharmonic and broadband signals extracted from the cavitation
noise spectra. The signals can be utilized to characterize different regimes of cavitation activity at
different acoustic power densities. When cavitation activity sets on, the aforementioned signals correlate
to fluctuations in the Schlieren contrast as well as the number of nucleated bubbles extracted from the
Schlieren Images. This additionally proves that signals extracted from cavitation noise spectra truly represent
a measure for cavitation activity. The cyclic behavior of cavitation activity is investigated and
related to the evolution of the bubble populations in the ultrasonic tank. It is shown that cavitation activity
is strongly linked to the occurrence of fast-moving bubbles. The origin of this ‘‘bubble streamers’’ is
investigated and their role in the initialization and propagation of cavitation activity throughout the sonicated
liquid is discussed. Finally, it is shown that bubble activity can be stabilized and enhanced by the
use of pulsed ultrasound by conserving and recycling active bubbles between subsequent pulsing cycles.status: publishe
Physical forces exerted by microbubbles on a surface in a traveling wave field
The effect of a wave with a varying traveling component on the bubble activity as well as the physical force generated by microbubbles on a surface has been studied. The acoustic emission from a collection of bubbles is measured in a 928 kHz sound field. Particle removal tests on a surface, which actually measures the applied physical force by the bubbles on that surface, indicate a very strong dependence on the angle of incidence. In other words, when the traveling wave component is maximized, the average physical force applied by microbubbles reaches a maximum. Almost complete particle removal for 78 nm silica particles was obtained for a traveling wave, while particle removal efficiency was reduced to only a few percent when a standing wave was applied. This increase in particle removal for a traveling wave is probably caused by a decrease in bubble trapping at nodes and antinodes in a standing wave field.publisher: Elsevier
articletitle: Physical forces exerted by microbubbles on a surface in a traveling wave field
journaltitle: Ultrasonics
articlelink: http://dx.doi.org/10.1016/j.ultras.2013.09.009
content_type: article
copyright: Copyright © 2013 Elsevier B.V. All rights reserved.status: publishe