113 research outputs found
Accelerated gas-liquid visible light photoredox catalysis with continuous-flow photochemical microreactors
In this protocol, we describe the construction and use of an operationally simple photochemical microreactor for gas-liquid photoredox catalysis using visible light. The general procedure includes details on how to set up the microreactor appropriately with inlets for gaseous reagents and organic starting materials, and it includes examples of how to use it to achieve continuous-flow preparation of disulfides or trifluoromethylated heterocycles and thiols. The reported photomicroreactors are modular, inexpensive and can be prepared rapidly from commercially available parts within 1 h even by nonspecialists. Interestingly, typical reaction times of gas-liquid visible light photocatalytic reactions performed in microflow are lower (in the minute range) than comparable reactions performed as a batch process (in the hour range). This can be attributed to the improved irradiation efficiency of the reaction mixture and the enhanced gas-liquid mass transfer in the segmented gas-liquid flow regime
Transit Photometry as an Exoplanet Discovery Method
Photometry with the transit method has arguably been the most successful
exoplanet discovery method to date. A short overview about the rise of that
method to its present status is given. The method's strength is the rich set of
parameters that can be obtained from transiting planets, in particular in
combination with radial velocity observations; the basic principles of these
parameters are given. The method has however also drawbacks, which are the low
probability that transits appear in randomly oriented planet systems, and the
presence of astrophysical phenomena that may mimic transits and give rise to
false detection positives. In the second part we outline the main factors that
determine the design of transit surveys, such as the size of the survey sample,
the temporal coverage, the detection precision, the sample brightness and the
methods to extract transit events from observed light curves. Lastly, an
overview over past, current and future transit surveys is given. For these
surveys we indicate their basic instrument configuration and their planet
catch, including the ranges of planet sizes and stellar magnitudes that were
encountered. Current and future transit detection experiments concentrate
primarily on bright or special targets, and we expect that the transit method
remains a principal driver of exoplanet science, through new discoveries to be
made and through the development of new generations of instruments.Comment: Review chapte
Recommended from our members
Long-term stellar activity variations and their effect on radial-velocity measurements
Long-term stellar activity variations can affect the detectability of
long-period and Earth-analogue extrasolar planets. We have, for 54 stars,
analysed the long-term trend of five activity indicators:
log, the cross-correlation function (CCF) bisector span, CCF
full-width-at-half-maximum, CCF contrast, and the area of the Gaussian fit to
the CCF; and studied their correlation with the RVs. The sign of the
correlations appears to vary as a function of stellar spectral type, and the
transition in sign signals a noteworthy change in the stellar activity
properties where earlier type stars appear more plage dominated. These
transitions become more clearly defined when considered as a function of the
convective zone depth. Therefore, it is the convective zone depth (which can be
altered by stellar metallicity) that appears to be the underlying fundamental
parameter driving the observed activity correlations. In addition, for most of
the stars, we find that the RVs become increasingly red-shifted as activity
levels increase, which can be explained by the increase in the suppression of
convective blue-shift. However, we also find a minority of stars where the RVs
become increasingly blue-shifted as activity levels increase. Finally, using
the correlation found between activity indicators and RVs, we removed RV
signals generated by long-term changes in stellar activity. We find that
performing simple cleaning of such long-term signals enables improved planet
detection at longer orbital periods
TRAPPIST-1: Global results of the Spitzer Exploration Science Program Red Worlds
With more than 1000 hours of observation from Feb 2016 to Oct 2019, the
Spitzer Exploration Program Red Worlds (ID: 13067, 13175 and 14223) exclusively
targeted TRAPPIST-1, a nearby (12pc) ultracool dwarf star orbited by seven
transiting Earth-sized planets, all well-suited for a detailed atmospheric
characterization with the upcoming JWST. In this paper, we present the global
results of the project. We analyzed 88 new transits and combined them with 100
previously analyzed transits, for a total of 188 transits observed at 3.6 or
4.5 m. We also analyzed 29 occultations (secondary eclipses) of planet b
and eight occultations of planet c observed at 4.5 m to constrain the
brightness temperatures of their daysides. We identify several orphan
transit-like structures in our Spitzer photometry, but all of them are of low
significance. We do not confirm any new transiting planets. We estimate for
TRAPPIST-1 transit depth measurements mean noise floors of 35 and 25 ppm
in channels 1 and 2 of Spitzer/IRAC, respectively. most of this noise floor is
of instrumental origins and due to the large inter-pixel inhomogeneity of IRAC
InSb arrays, and that the much better interpixel homogeneity of JWST
instruments should result in noise floors as low as 10ppm, which is low enough
to enable the atmospheric characterization of the planets by transit
transmission spectroscopy. We construct updated broadband transmission spectra
for all seven planets which show consistent transit depths between the two
Spitzer channels. We identify and model five distinct high energy flares in the
whole dataset, and discuss our results in the context of habitability. Finally,
we fail to detect occultation signals of planets b and c at 4.5 m, and can
only set 3 upper limits on their dayside brightness temperatures (611K
for b 586K for c)
Development of the SPECULOOS exoplanet search project
SPECULOOS (Search for habitable Planets EClipsing ULtra-cOOl Stars) aims to
perform a transit search on the nearest (pc) ultracool (K) dwarf
stars. The project's main motivation is to discover potentially habitable
planets well-suited for detailed atmospheric characterisation with upcoming
giant telescopes, like the James Webb Space Telescope (JWST) and European Large
Telescope (ELT). The project is based on a network of 1m robotic telescopes,
namely the four ones of the SPECULOOS-Southern Observatory (SSO) in Cerro
Paranal, Chile, one telescope of the SPECULOOS-Northern Observatory (SNO) in
Tenerife, and the SAINT-Ex telescope in San Pedro M\'artir, Mexico. The
prototype survey of the SPECULOOS project on the 60~cm TRAPPIST telescope
(Chile) discovered the TRAPPIST-1 system, composed of seven temperate
Earth-sized planets orbiting a nearby (12~pc) Jupiter-sized star. In this
paper, we review the current status of SPECULOOS, its first results, the plans
for its development, and its connection to the Transiting Exoplanet Survey
Satellite (TESS) and JWST
NGTS-13b: A hot 4.8 Jupiter-mass planet transiting a subgiant star
We report the discovery of the massive hot Jupiter NGTS-13b by the Next
Generation Transit Survey (NGTS). The V = 12.7 host star is likely in the
subgiant evolutionary phase with log g = 4.04 0.05, T =
5819 73 K, M = 1.30 M, and R =
1.79 0.06 R. NGTS detected a transiting planet with a period of
P = 4.12 days around the star, which was later validated with the Transiting
Exoplanet Survey Satellite (TESS; TIC 454069765). We confirm the planet using
radial velocities from the CORALIE spectrograph. Using NGTS and TESS full-frame
image photometry combined with CORALIE radial velocities we determine NGTS-13b
to have a radius of R = 1.142 0.046 R, mass of M =
4.84 0.44 M and eccentricity e = 0.086 0.034. Some previous
studies suggest that 4 M may be a border between two separate
formation scenarios (e.g., core accretion and disk instability) and that
massive giant planets share similar formation mechanisms as lower-mass brown
dwarfs. NGTS-13b is just above 4 M making it an important addition to
the statistical sample needed to understand the differences between various
classes of substellar companions. The high metallicity, [Fe/H] = 0.25
0.17, of NGTS-13 does not support previous suggestions that massive giants are
found preferentially around lower metallicity host stars, but NGTS-13b does
support findings that more massive and evolved hosts may have a higher
occurrence of close-in massive planets than lower-mass unevolved stars
NGTS-5b: A highly inflated planet offering insights into the sub-Jovian desert
Context: Planetary population analysis gives us insight into formation and
evolution processes. For short-period planets, the subJovian desert has been
discussed in recent years with regard to the planet population in the
mass/period and radius/period parameter space without taking stellar parameters
into account. The Next Generation Transit Survey (NGTS) is optimised for
detecting planets in this regime, which allows for further analysis of the
sub-Jovian desert.
Aims: With high-precision photometric surveys (e.g. with NGTS and TESS),
which aim to detect short period planets especially around M/K-type host stars,
stellar parameters need to be accounted for when empirical data are compared to
model predictions. Presenting a newly discovered planet at the boundary of the
sub-Jovian desert, we analyse its bulk properties and use it to show the
properties of exoplanets that border the sub-Jovian desert.
Methods: Using NGTS light curve and spectroscopic follow-up observations, we
confirm the planetary nature of planet NGTS-5b and determine its mass. Using
exoplanet archives, we set the planet in context with other discoveries.
Results: NGTS-5b is a short-period planet with an orbital period of 3.3569866
+- 0.0000026 days. With a mass of 0.229 +- 0.037 MJup and a radius of 1.136 +-
0.023 RJup, it is highly inflated. Its mass places it at the upper boundary of
the sub-Jovian desert. Because the host is a K2 dwarf, we need to account for
the stellar parameters when NGTS-5b is analysed with regard to planet
populations.
Conclusions: With red-sensitive surveys (e.g. with NGTS and TESS), we expect
many more planets around late-type stars to be detected. An empirical analysis
of the sub-Jovian desert should therefore take stellar parameters into account
NGTS discovery of a highly inflated Saturn-mass planet and a highly irradiated hot Jupiter: NGTS-26 b and NGTS-27 b
We report the discovery of two new transiting giant exoplanets NGTS-26 b and NGTS-27 b by the Next Generation Transit Survey (NGTS). NGTS-26 b orbits around a G6-type main sequence star every 4.52 days. It has a mass of 0.29-0.06+0.07 MJup and a radius of 1.33-0.05+0.06 RJup making it a Saturn-mass planet with a highly inflated radius. NGTS-27 b orbits around a slightly evolved G3-type star every 3.37 days. It has a mass of 0.59-0.07+0.10 MJup and a radius of 1.40±0.04 RJup, making it a relatively standard hot Jupiter. The transits of these two planetary systems were re-observed and confirmed in photometry by the SAAO 1.0-m telescope, 1.2-m Euler Swiss telescope as well as the TESS spacecraft, and their masses were derived spectroscopically by the CORALIE, FEROS and HARPS spectrographs. Both giant exoplanets are highly irradiated by their host stars and present an anomalously inflated radius, especially NGTS-26 b which is one of the largest objects among peers of similar mass
NGTS-11 b (TOI-1847 b): A Transiting Warm Saturn Recovered from a TESS Single-transit Event
We report the discovery of NGTS-11 b (=TOI-1847 b), a transiting Saturn in a
35.46-day orbit around a mid K-type star (Teff=5050 K). We initially identified
the system from a single-transit event in a TESS full-frame image light-curve.
Following seventy-nine nights of photometric monitoring with an NGTS telescope,
we observed a second full transit of NGTS-11 b approximately one year after the
TESS single-transit event. The NGTS transit confirmed the parameters of the
transit signal and restricted the orbital period to a set of 13 discrete
periods. We combined our transit detections with precise radial velocity
measurements to determine the true orbital period and measure the mass of the
planet. We find NGTS-11 b has a radius of 0.817+0.028-0.032 , a mass of
0.344+0.092-0.073 , and an equilibrium temperature of just 435+34-32 K,
making it one of the coolest known transiting gas giants. NGTS-11 b is the
first exoplanet to be discovered after being initially identified as a TESS
single-transit event, and its discovery highlights the power of intense
photometric monitoring in recovering longer-period transiting exoplanets from
single-transit events
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