10 research outputs found
A citation history of measurements of Newtons constant of Gravity
We created and analyzed a citation history of papers covering measurements of
Newtons constant of gravity from 1686 to 2016. Interest concerning the true
value of the gravitational constant was most intense in the late 90s to early
2000s and is gaining traction again in the present. Another network consisting
of the same papers was created using citations from databases to display the
prominence of papers on Newtons constant in the wider scientific community. In
general, papers that were important in one network remained important in the
other while papers that had little importance in one network remained
unimportant in the other. The US contributes the most to literature on the
topic both in where journals were published and where the work was done;
however, many other countries, such as China, Russia, France, Germany,
Switzerland, and the UK also provide many papers on Newtons G. Work done within
certain countries tends to be considered more important and cited more often
within that country. Recent efforts promoting international collaboration may
have an impact on this trend
On-sky speckle nulling through a single-mode fiber with the Keck Planet Imager and Characterizer
The Keck Planet Imager and Characterizer (KPIC) is an instrument at the Keck
II telescope that enables high-resolution spectroscopy of directly imaged
exoplanets and substellar companions. KPIC uses single-mode fibers to couple
the adaptive optics system to Keck's near-infrared spectrometer (NIRSPEC).
However, KPIC's sensitivity at small separations is limited by the leakage of
stellar light into the fiber. Speckle nulling uses a deformable mirror to
destructively interfere starlight with itself, a technique typically used to
reduce stellar signal on a focal-plane imaging detector. We present the first
on-sky demonstration of speckle nulling through an optical fiber with KPIC,
using NIRSPEC to collect exposures that measure speckle phase for
quasi-real-time wavefront control while also serving as science data. We repeat
iterations of measurement and correction, each using at least 5 exposures. We
show a decrease in the on-sky leaked starlight by a factor of 2.6 to 2.8 in the
targeted spectral order, at a spatial separation of 2.0 {\lambda}/D in K-band.
This corresponds to an estimated factor of 2.6 to 2.8 decrease in the required
exposure time to reach a given SNR, relative to conventional KPIC observations.
The performance of speckle nulling is limited by instability in the speckle
phase: when the loop is opened, the null-depth degrades by a factor of 2 on the
timescale of a single phase measurement, which would limit the suppression that
can be achieved. Future work includes exploring gradient-descent methods, which
may be faster and thereby able to achieve deeper nulls. In the meantime, the
speckle nulling algorithm demonstrated in this work can be used to decrease
stellar leakage and improve the signal-to-noise of science observations.Comment: 18 pages, 4 figure
The MOSDEF Survey: Differences in SFR and Metallicity for Morphologically-Selected Mergers at z~2
We study the properties of 55 morphologically-identified merging galaxy
systems at z~2. These systems are flagged as mergers based on features such as
tidal tails, double nuclei, and asymmetry. Our sample is drawn from the MOSFIRE
Deep Evolution Field (MOSDEF) survey, along with a control sample of isolated
galaxies at the same redshift. We consider the relationships between stellar
mass, star formation rate (SFR), and gas-phase metallicity for both merging and
non-merging systems. In the local universe, merging systems are characterized
by an elevated SFR and depressed metallicity compared to isolated systems at a
given mass. Our results indicate SFR enhancement and metallicity deficit for
merging systems relative to non-merging systems for a fixed stellar mass at
z~2, though larger samples are required to establish these preliminary results
with higher statistical significance. In future work, it will be important to
establish if the enhanced SFR and depressed metallicity in high-redshift
mergers deviate from the "fundamental metallicity relation," as is observed in
mergers in the local universe, and therefore shed light on gas flows during
galaxy interactions.Comment: 9 pages, 5 figures, 5 figures, accepted to MNRA
The MOSDEF Survey: Differences in SFR and Metallicity for Morphologically-Selected Mergers at z ~ 2
We study the properties of 55 morphologically-identified merging galaxy systems at z ~ 2. These systems are flagged as mergers based on features such as tidal tails, double nuclei, and asymmetry. Our sample is drawn from the MOSFIRE Deep Evolution Field (MOSDEF) survey, along with a control sample of isolated galaxies at the same redshift. We consider the relationships between stellar mass, star formation rate (SFR), and gas-phase metallicity for both merging and non-merging systems. In the local universe, merging systems are characterized by an elevated SFR and depressed metallicity compared to isolated systems at a given mass. Our results indicate SFR enhancement and metallicity deficit for merging systems relative to non-merging systems for a fixed stellar mass at z ~ 2, though larger samples are required to establish these preliminary results with higher statistical significance. In future work, it will be important to establish if the enhanced SFR and depressed metallicity in high-redshift mergers deviate from the "fundamental metallicity relation," as is observed in mergers in the local universe, and therefore shed light on gas flows during galaxy interactions
Vortex Fiber Nulling for Exoplanet Observations: Implementation and First Light
Vortex fiber nulling (VFN) is a single-aperture interferometric technique for
detecting and characterizing exoplanets separated from their host star by less
than a diffracted beam width. VFN uses a vortex mask and single mode fiber to
selectively reject starlight while coupling off-axis planet light with a simple
optical design that can be readily implemented on existing direct imaging
instruments that can feed light to an optical fiber. With its axially symmetric
coupling region peaking within the inner working angle of conventional
coronagraphs, VFN is more efficient at detecting new companions at small
separations than conventional direct imaging, thereby increasing the yield of
on-going exoplanet search campaigns. We deployed a VFN mode operating in K band
(m) on the Keck Planet Imager and Characterizer (KPIC)
instrument at the Keck II Telescope. In this paper we present the instrument
design of this first on-sky demonstration of VFN and the results from on-sky
commissioning, including planet and star throughput measurements and predicted
flux-ratio detection limits for close-in companions. The instrument performance
is shown to be sufficient for detecting a companion times fainter than a
magnitude host star in 1 hour at a separation of 50 mas
(1.1). This makes the instrument capable of efficiently detecting
substellar companions around young stars. We also discuss several routes for
improvement that will reduce the required integration time for a detection by a
factor 3.Comment: 26 pages, 5 figures; Accepted to JATI
A Clear View of a Cloudy Brown Dwarf Companion from High-Resolution Spectroscopy
Direct imaging studies have mainly used low-resolution spectroscopy
() to study the atmospheres of giant exoplanets and brown dwarf
companions, but the presence of clouds has often led to degeneracies in the
retrieved atmospheric abundances (e.g. C/O, metallicity). This precludes clear
insights into the formation mechanisms of these companions. The Keck Planet
Imager and Characterizer (KPIC) uses adaptive optics and single-mode fibers to
transport light into NIRSPEC ( in band), and aims to address
these challenges with high-resolution spectroscopy. Using an atmospheric
retrieval framework based on petitRADTRANS, we analyze KPIC high-resolution
spectrum (m) and archival low-resolution spectrum (m)
of the benchmark brown dwarf HD 4747 B (,
au, K). We find that our measured C/O
and metallicity for the companion from the KPIC high-resolution spectrum agree
with that of its host star within . The retrieved parameters from
the band high-resolution spectrum are also independent of our choice of
cloud model. In contrast, the retrieved parameters from the low-resolution
spectrum are highly sensitive to our chosen cloud model. Finally, we detect CO,
HO, and CH (volume mixing ratio of log(CH)=) in this
L/T transition companion with the KPIC data. The relative molecular abundances
allow us to constrain the degree of chemical disequilibrium in the atmosphere
of HD 4747 B, and infer a vertical diffusion coefficient that is at the upper
limit predicted from mixing length theory.Comment: 33 pages, 16 figures, Accepted to Ap
Recommended from our members
A citation history of measurements of Newton's constant of gravity
Detecting Exomoons from Radial Velocity Measurements of Self-luminous Planets: Application to Observations of HR 7672 B and Future Prospects
The detection of satellites around extrasolar planets, so called exomoons, remains a largely unexplored territory. In this work, we study the potential of detecting these elusive objects from radial velocity monitoring of self-luminous, directly imaged planets. This technique is now possible thanks to the development of dedicated instruments combining the power of high-resolution spectroscopy and high-contrast imaging. First, we demonstrate a sensitivity to satellites with a mass ratio of 1%–4% at separations similar to the Galilean moons from observations of a brown-dwarf companion (HR 7672 B; K _mag = 13; 0.″7 separation) with the Keck Planet Imager and Characterizer ( R ∼ 35,000 in the K band) at the W. M. Keck Observatory. Current instrumentation is therefore already sensitive to large unresolved satellites that could be forming from gravitational instability akin to binary star formation. Using end-to-end simulations, we then estimate that future instruments such as the Multi-Object Diffraction-limited High-resolution Infrared Spectrograph, planned for the Thirty Meter Telescope, should be sensitive to satellites with mass ratios of ∼10 ^−4 . Such small moons would likely form in a circumplanetary disk similar to the Jovian satellites in the solar system. Looking for the Rossiter–McLaughlin effect could also be an interesting pathway to detecting the smallest moons on short orbital periods. Future exomoon discoveries will allow precise mass measurements of the substellar companions that they orbit and provide key insight into the formation of exoplanets. They would also help constrain the population of habitable Earth-sized moons orbiting gas giants in the habitable zone of their stars
Validation of Elemental and Isotopic Abundances in Late-M Spectral Types with the Benchmark HIP 55507 AB System
M dwarfs are common host stars to exoplanets but often lack atmospheric abundance measurements. Late-M dwarfs are also good analogs to the youngest substellar companions, which share similar T _eff ∼ 2300–2800 K. We present atmospheric analyses for the M7.5 companion HIP 55507 B and its K6V primary star with Keck/KPIC high-resolution ( R ∼ 35,000) K -band spectroscopy. First, by including KPIC relative radial velocities between the primary and secondary in the orbit fit, we improve the dynamical mass precision by 60% and find , putting HIP 55507 B above the stellar–substellar boundary. We also find that HIP 55507 B orbits its K6V primary star with au and e = 0.40 ± 0.04. From atmospheric retrievals of HIP 55507 B, we measure [C/H] = 0.24 ± 0.13, [O/H] = 0.15 ± 0.13, and C/O = 0.67 ± 0.04. Moreover, we strongly detect ^13 CO (7.8 σ significance) and tentatively detect (3.7 σ significance) in the companion’s atmosphere and measure and after accounting for systematic errors. From a simplified retrieval analysis of HIP 55507 A, we measure and for the primary star. These results demonstrate that HIP 55507 A and B have consistent ^12 C/ ^13 C and ^16 O/ ^18 O to the <1 σ level, as expected for a chemically homogeneous binary system. Given the similar flux ratios and separations between HIP 55507 AB and systems with young substellar companions, our results open the door to systematically measuring ^13 CO and abundances in the atmospheres of substellar or even planetary-mass companions with similar spectral types