273 research outputs found
Preparation & Characterization of Dimethylformamidyl Substituted Titanium( IV) Compounds
456-45
Constraints on Metastable Helium in the Atmospheres of WASP-69b and WASP-52b with Ultra-Narrowband Photometry
Infrared observations of metastable 2S helium absorption with ground- and
space-based spectroscopy are rapidly maturing, as this species is a unique
probe of exoplanet atmospheres. Specifically, the transit depth in the triplet
feature (with vacuum wavelengths near 1083.3 nm) can be used to constrain the
temperature and mass loss rate of an exoplanet's upper atmosphere. Here, we
present a new photometric technique to measure metastable 2S helium
absorption using an ultra-narrowband filter (full-width at half-maximum of
0.635 nm) coupled to a beam-shaping diffuser installed in the Wide-field
Infrared Camera (WIRC) on the 200-inch Hale Telescope at Palomar Observatory.
We use telluric OH lines and a helium arc lamp to characterize refractive
effects through the filter and to confirm our understanding of the filter
transmission profile. We benchmark our new technique by observing a transit of
WASP-69b and detect an excess absorption of % (11.1),
consistent with previous measurements after considering our bandpass. Then, we
use this method to study the inflated gas giant WASP-52b and place a
95th-percentile upper limit on excess absorption in our helium bandpass of
0.47%. Using an atmospheric escape model, we constrain the mass loss rate for
WASP-69b to be
() at 7,000 K
(12,000 K). Additionally, we set an upper limit on the mass loss rate of
WASP-52b at these temperatures of
(). These results show that
ultra-narrowband photometry can reliably quantify absorption in the metastable
helium feature.Comment: 17 pages, 8 figures (figures 1 and 2 are rasterized for arXiv file
size compliance), accepted to A
A Giant Glitch in the Energetic 69 ms X-ray Pulsar AXS J161730-505505
We present new results on the recently discovered 69 ms X-ray pulsar AXS
J161730-505505, the sixth youngest sample of all known pulsars. We have
undertaken a comprehensive X-ray observing campaign of AXS J161730-505505 with
the ASCA, SAX, and XTE observatories and follow its long term spin-down history
between 1989 and 1999, using these, archival GINGA and ASCA data sets, and the
radio ephemeris. The spin-down is not simply described by a linear function as
originally thought, but instead we find evidence of a giant glitch (|Delta P/P|
> 10E-6) between 1993 August and 1997 September, perhaps the largest yet
observed from a young pulsar. The glitch is well described by steps in the
period and its first derivative accompanied by a persistent second derivative
similar to those in the Vela pulsar. The pulse profile of AXS J161730-505505
presents a single asymmetric peak which is maintained over all observation
epochs. The energy spectrum is also steady over time, characterized by a highly
absorbed power-law with a photon index 1.4 +/- 0.2, consistent with that found
for other young rotation powered pulsars.Comment: 6 pages with 2 figures, LaTex, emulateapj.sty. To appear in the
Astrophysical Journal Letter
Optical and Infrared Observations of SGR 1806-20
The soft gamma-ray repeater (SGR) 180620 is associated with the
center-brightened non-thermal nebula G~10.00.3, thought to be a plerion. As
in other plerions, a steady \Xray\ source, AX~1805.72025, has been detected
coincident with the peak of the nebular radio emission. Vasisht et al.\ have
shown that the radio peak has a core-jet appearance, and argue that the core
marks the true position of the SGR. At optical wavelengths, we detect three
objects in the vicinity of the radio core. Only for the star closest to the
core, barely visible in the optical but bright in the infrared (mag.),
the reddening is consistent with the high extinction (mag.) that
has been inferred for AX~1805.72025. From the absence of CO band absorption,
we infer that the spectral type of this star is earlier than late~G/early~K.
The large extinction probably arises in a molecular cloud located at a distance
of 6kpc, which means that the star, just like AX~1805.72025, is in or
behind this cloud. This implies that the star is a supergiant. Since
supergiants are rare, a chance coincidence with the compact radio core is very
unlikely. To our knowledge, there are only three other examples of luminous
stars embedded in non-thermal radio nebulae, SS~433, \mbox{Cir X-1} and
G~70.7+1.2. Given this and the low coincidence probability, we suggest that the
bright star is physically associated with SGR~180620, making it the first
stellar identification of a high-energy transient.Comment: 7 pages, AASTeX (needs LaTeX style files aaspptwo.sty and epsf.sty,
plus PostScript figure). In case of problems, contact [email protected]
Observing Exoplanets with High-Dispersion Coronagraphy. II. Demonstration of an Active Single-Mode Fiber Injection Unit
High-dispersion coronagraphy (HDC) optimally combines high contrast imaging
techniques such as adaptive optics/wavefront control plus coronagraphy to high
spectral resolution spectroscopy. HDC is a critical pathway towards fully
characterizing exoplanet atmospheres across a broad range of masses from giant
gaseous planets down to Earth-like planets. In addition to determining the
molecular composition of exoplanet atmospheres, HDC also enables Doppler
mapping of atmosphere inhomogeneities (temperature, clouds, wind), as well as
precise measurements of exoplanet rotational velocities. Here, we demonstrate
an innovative concept for injecting the directly-imaged planet light into a
single-mode fiber, linking a high-contrast adaptively-corrected coronagraph to
a high-resolution spectrograph (diffraction-limited or not). Our laboratory
demonstration includes three key milestones: close-to-theoretical injection
efficiency, accurate pointing and tracking, on-fiber coherent modulation and
speckle nulling of spurious starlight signal coupling into the fiber. Using the
extreme modal selectivity of single-mode fibers, we also demonstrated speckle
suppression gains that outperform conventional image-based speckle nulling by
at least two orders of magnitude.Comment: 10 pages, 7 figures, accepted by Ap
- …