11 research outputs found
Astro2020 White Paper: A Direct Measure of Cosmic Acceleration
Nearly a century after the discovery that we live in an expanding Universe,
and two decades after the discovery of accelerating cosmic expansion, there
remains no direct detection of this acceleration via redshift drift - a change
in the cosmological expansion velocity versus time. Because cosmological
redshift drift directly determines the Hubble parameter H(z), it is arguably
the cleanest possible measurement of the expansion history, and has the
potential to constrain dark energy models (e.g. Kim et al. 2015). The challenge
is that the signal is small - the best observational constraint presently has
an uncertainty several orders of magnitude larger than the expected signal
(Darling 2012). Nonetheless, direct detection of redshift drift is becoming
feasible, with upcoming facilities such as the ESO-ELT and SKA projecting
possible detection within two to three decades. This timescale is uncomfortably
long given the potential of this cosmological test. With dedicated experiments
it should be possible to rapidly accelerate progress and detect redshift drift
with only a five-year observational baseline. Such a facility would also be
ideal for precision radial velocity measurements of exoplanets, which could be
obtained as a byproduct of the ongoing calibration measurements for the
experiment.Comment: White paper submitted to the Astro2020 Decadal Survey. 6 page
Forecasting cosmic acceleration measurements using the Lyman- forest
We present results from end-to-end simulations of observations designed to
constrain the rate of change in the expansion history of the Universe using the
redshift drift of the Lyman- forest absorption lines along the
lines-of-sight toward bright quasars. For our simulations we take
Lyman- forest lines extracted from Keck/HIRES spectra of bright quasars
at , and compare the results from these real quasar spectra with mock
spectra generated via Monte Carlo realizations. We use the results of these
simulations to assess the potential for a dedicated observatory to detect
redshift drift, and quantify the telescope and spectrograph requirements for
these observations. Relative to Liske et al. (2008), two main refinements in
the current work are inclusion of quasars from more recent catalogs and
consideration of a realistic observing strategy for a dedicated redshift drift
experiment that maximizes . We find that using a
dedicated facility and our designed observing plan, the redshift drift can be
detected at significance in 15 years with a 25m telescope, given a
spectrograph with long term stability with and 25% total system
efficiency. To achieve this significance, the optimal number of targets is four
quasars, with observing time weighted based upon and
object visibility. This optimized strategy leads to a 9% decrease in the
telescope diameter or a 6% decrease in the required time to achieve the same
S/N as for the idealized case of uniformly distributing time to the same
quasars.Comment: 13 pages, 12 figures, accepted for publication in MNRA
Astro2020 Project White Paper: The Cosmic Accelerometer
We propose an experiment, the Cosmic Accelerometer, designed to yield
velocity precision of cm/s with measurement stability over years to
decades. The first-phase Cosmic Accelerometer, which is at the scale of the
Astro2020 Small programs, will be ideal for precision radial velocity
measurements of terrestrial exoplanets in the Habitable Zone of Sun-like stars.
At the same time, this experiment will serve as the technical pathfinder and
facility core for a second-phase larger facility at the Medium scale, which can
provide a significant detection of cosmological redshift drift on a 6-year
timescale. This larger facility will naturally provide further detection/study
of Earth twin planet systems as part of its external calibration process. This
experiment is fundamentally enabled by a novel low-cost telescope technology
called PolyOculus, which harnesses recent advances in commercial off the shelf
equipment (telescopes, CCD cameras, and control computers) combined with a
novel optical architecture to produce telescope collecting areas equivalent to
standard telescopes with large mirror diameters. Combining a PolyOculus array
with an actively-stabilized high-precision radial velocity spectrograph
provides a unique facility with novel calibration features to achieve the
performance requirements for the Cosmic Accelerometer
The first super-Earth Detection from the High Cadence and High Radial Velocity Precision Dharma Planet Survey
The Dharma Planet Survey (DPS) aims to monitor about 150 nearby very bright
FGKM dwarfs (within 50 pc) during 20162020 for low-mass planet detection and
characterization using the TOU very high resolution optical spectrograph
(R100,000, 380-900nm). TOU was initially mounted to the 2-m Automatic
Spectroscopic Telescope at Fairborn Observatory in 2013-2015 to conduct a pilot
survey, then moved to the dedicated 50-inch automatic telescope on Mt. Lemmon
in 2016 to launch the survey. Here we report the first planet detection from
DPS, a super-Earth candidate orbiting a bright K dwarf star, HD 26965. It is
the second brightest star ( mag) on the sky with a super-Earth
candidate. The planet candidate has a mass of 8.47,
period of d, and eccentricity of . This RV
signal was independently detected by Diaz et al. (2018), but they could not
confirm if the signal is from a planet or from stellar activity. The orbital
period of the planet is close to the rotation period of the star (3944.5 d)
measured from stellar activity indicators. Our high precision photometric
campaign and line bisector analysis of this star do not find any significant
variations at the orbital period. Stellar RV jitters modeled from star spots
and convection inhibition are also not strong enough to explain the RV signal
detected. After further comparing RV data from the star's active magnetic phase
and quiet magnetic phase, we conclude that the RV signal is due to
planetary-reflex motion and not stellar activity.Comment: 13 pages, 17 figures, Accepted for publication in MNRA
The first super-Earth detection from the high cadence and high radial velocity precision Dharma Planet Survey
The Dharma Planet Survey (DPS) aims to monitor about 150 nearby very bright FGKM dwarfs (within 50 pc) during 2016–2020 for low-mass planet detection and characterization using the TOU very high resolution optical spectrograph (R≈100000, 380–900 nm). TOU was initially mounted to the 2-m Automatic Spectroscopic Telescope at Fairborn Observatory in 2013–2015 to conduct a pilot survey, then moved to the dedicated 50-inch automatic telescope on Mt. Lemmon in 2016 to launch the survey. Here, we report the first planet detection from DPS, a super-Earth candidate orbiting a bright K dwarf star, HD 26965. It is the second brightest star (V = 4.4 mag) on the sky with a super-Earth candidate. The planet candidate has a mass of 8.47 ± 0.47MEarth, period of 42.38 ± 0.01 d, and eccentricity of 0.04+0.05−0.03. This radial velocity (RV) signal was independently detected by Díaz et al., but they could not confirm if the signal is from a planet or stellar activity. The orbital period of the planet is close to the rotation period of the star (39–44.5 d) measured from stellar activity indicators. Our high precision photometric campaign and line bisector analysis of this star do not find any significant variations at the orbital period. Stellar RV jitters modelled from star-spots and convection inhibition are also not strong enough to explain the RV signal detected. After further comparing RV data from the star’s active magnetic phase and quiet magnetic phase, we conclude that the RV signal is due to planetary-reflex motion and not stellar activity
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Astro2020 White Paper: A Direct Measure of Cosmic Acceleration
Nearly a century after the discovery that we live in an expanding Universe,
and two decades after the discovery of accelerating cosmic expansion, there
remains no direct detection of this acceleration via redshift drift - a change
in the cosmological expansion velocity versus time. Because cosmological
redshift drift directly determines the Hubble parameter H(z), it is arguably
the cleanest possible measurement of the expansion history, and has the
potential to constrain dark energy models (e.g. Kim et al. 2015). The challenge
is that the signal is small - the best observational constraint presently has
an uncertainty several orders of magnitude larger than the expected signal
(Darling 2012). Nonetheless, direct detection of redshift drift is becoming
feasible, with upcoming facilities such as the ESO-ELT and SKA projecting
possible detection within two to three decades. This timescale is uncomfortably
long given the potential of this cosmological test. With dedicated experiments
it should be possible to rapidly accelerate progress and detect redshift drift
with only a five-year observational baseline. Such a facility would also be
ideal for precision radial velocity measurements of exoplanets, which could be
obtained as a byproduct of the ongoing calibration measurements for the
experiment
Recommended from our members
Astro2020 Project White Paper: The Cosmic Accelerometer
We propose an experiment, the Cosmic Accelerometer, designed to yield
velocity precision of cm/s with measurement stability over years to
decades. The first-phase Cosmic Accelerometer, which is at the scale of the
Astro2020 Small programs, will be ideal for precision radial velocity
measurements of terrestrial exoplanets in the Habitable Zone of Sun-like stars.
At the same time, this experiment will serve as the technical pathfinder and
facility core for a second-phase larger facility at the Medium scale, which can
provide a significant detection of cosmological redshift drift on a 6-year
timescale. This larger facility will naturally provide further detection/study
of Earth twin planet systems as part of its external calibration process. This
experiment is fundamentally enabled by a novel low-cost telescope technology
called PolyOculus, which harnesses recent advances in commercial off the shelf
equipment (telescopes, CCD cameras, and control computers) combined with a
novel optical architecture to produce telescope collecting areas equivalent to
standard telescopes with large mirror diameters. Combining a PolyOculus array
with an actively-stabilized high-precision radial velocity spectrograph
provides a unique facility with novel calibration features to achieve the
performance requirements for the Cosmic Accelerometer