111 research outputs found
PynPoint: a modular pipeline architecture for processing and analysis of high-contrast imaging data
The direct detection and characterization of planetary and substellar
companions at small angular separations is a rapidly advancing field. Dedicated
high-contrast imaging instruments deliver unprecedented sensitivity, enabling
detailed insights into the atmospheres of young low-mass companions. In
addition, improvements in data reduction and PSF subtraction algorithms are
equally relevant for maximizing the scientific yield, both from new and
archival data sets. We aim at developing a generic and modular data reduction
pipeline for processing and analysis of high-contrast imaging data obtained
with pupil-stabilized observations. The package should be scalable and robust
for future implementations and in particular well suitable for the 3-5 micron
wavelength range where typically (ten) thousands of frames have to be processed
and an accurate subtraction of the thermal background emission is critical.
PynPoint is written in Python 2.7 and applies various image processing
techniques, as well as statistical tools for analyzing the data, building on
open-source Python packages. The current version of PynPoint has evolved from
an earlier version that was developed as a PSF subtraction tool based on PCA.
The architecture of PynPoint has been redesigned with the core functionalities
decoupled from the pipeline modules. Modules have been implemented for
dedicated processing and analysis steps, including background subtraction,
frame registration, PSF subtraction, photometric and astrometric measurements,
and estimation of detection limits. The pipeline package enables end-to-end
data reduction of pupil-stabilized data and supports classical dithering and
coronagraphic data sets. As an example, we processed archival VLT/NACO L' and
M' data of beta Pic b and reassessed the planet's brightness and position with
an MCMC analysis, and we provide a derivation of the photometric error budget.Comment: 16 pages, 9 figures, accepted for publication in A&A, PynPoint is
available at https://github.com/PynPoint/PynPoin
Widespread Shocks in the Nucleus of NGC 404 Revealed by Near-infrared Integral Field Spectroscopy
We present high spatial resolution, integral field spectrograph (IFS) observations of the nearby low-ionization nuclear emission-line region (LINER) galaxy NGC 404 at 1.25 μm (J band) and 2.2 μm (K band) near-infrared (NIR) wavelengths. Although NGC 404 is thought to host an intermediate-mass black hole (BH) at its center, it has been unclear whether accretion onto the BH or another mechanism such as shock excitation drives its LINER emission at optical/NIR wavelengths. We use the OSIRIS IFS at Keck Observatory behind laser guide star adaptive optics to map the strength and kinematics of [Fe ii], H_2, and hydrogen recombination lines at spatial resolutions of 1 pc across the central 30 pc of the galaxy. The H_2 gas is in a central rotating disk, and ratios of multiple H_2 lines indicate that the molecular gas is thermally excited, with some contribution from UV fluorescence. The [Fe ii] emission is more extended and diffuse than the molecular gas and has a different kinematic structure that reaches higher velocities/dispersions. We also map the strength of the CO stellar absorption feature and constrain the dominant age of the nuclear stellar population to ~1 Gyr. Finally, we find regions across the nucleus of NGC 404 with [Fe ii]/Paβ line ratios up to 6.5, ~2.5 times higher than the ratio measured from spatially integrated spectra. From these high line ratios, we conclude that shocks are the dominant physical mechanism exciting NGC 404's LINER emission and argue that a possible source of this shock excitation is a supernova remnant
The Shortest Known Period Star Orbiting our Galaxy's Supermassive Black Hole
Stars with short orbital periods at the center of our galaxy offer a powerful
and unique probe of a supermassive black hole. Over the past 17 years, the W.
M. Keck Observatory has been used to image the Galactic center at the highest
angular resolution possible today. By adding to this data set and advancing
methodologies, we have detected S0-102, a star orbiting our galaxy's
supermassive black hole with a period of just 11.5 years. S0-102 doubles the
number of stars with full phase coverage and periods less than 20 years. It
thereby provides the opportunity with future measurements to resolve
degeneracies in the parameters describing the central gravitational potential
and to test Einstein's theory of General Relativity in an unexplored regime.Comment: Science, in press (published Oct 5, 2012). See Science Online for the
Supplementary Material, or here:
http://www.astro.ucla.edu/~ghezgroup/gc/research/S02_S0102_orbits.htm
The Keplerian orbit of G2
We give an update of the observations and analysis of G2 - the gaseous red
emission-line object that is on a very eccentric orbit around the Galaxy's
central black hole and predicted to come within 2400 Rs in early 2014. During
2013, the laser guide star adaptive optics systems on the W. M. Keck I and II
telescopes were used to obtain three epochs of spectroscopy and imaging at the
highest spatial resolution currently possible in the near-IR. The updated
orbital solution derived from radial velocities in addition to Br-Gamma line
astrometry is consistent with our earlier estimates. Strikingly, even ~6 months
before pericenter passage there is no perceptible deviation from a Keplerian
orbit. We furthermore show that a proposed "tail" of G2 is likely not
associated with it but is rather an independent gas structure. We also show
that G2 does not seem to be unique, since several red emission-line objects can
be found in the central arcsecond. Taken together, it seems more likely that G2
is ultimately stellar in nature, although there is clearly gas associated with
it.Comment: Proceedings of IAU Symposium #303, "The Galactic Center: Feeding and
Feedback in a Normal Galactic Nucleus"; 2013 September 30 - October 4, Santa
Fe New Mexico (USA
An Improved Distance and Mass Estimate for Sgr A* from a Multistar Orbit Analysis
We present new, more precise measurements of the mass and distance of our
Galaxy's central supermassive black hole, Sgr A*. These results stem from a new
analysis that more than doubles the time baseline for astrometry of faint stars
orbiting Sgr A*, combining two decades of speckle imaging and adaptive optics
data. Specifically, we improve our analysis of the speckle images by using
information about a star's orbit from the deep adaptive optics data (2005 -
2013) to inform the search for the star in the speckle years (1995 - 2005).
When this new analysis technique is combined with the first complete
re-reduction of Keck Galactic Center speckle images using speckle holography,
we are able to track the short-period star S0-38 (K-band magnitude = 17,
orbital period = 19 years) through the speckle years. We use the kinematic
measurements from speckle holography and adaptive optics to estimate the orbits
of S0-38 and S0-2 and thereby improve our constraints of the mass ()
and distance () of Sgr A*: and kpc. The
uncertainties in and as determined by the combined orbital fit
of S0-2 and S0-38 are improved by a factor of 2 and 2.5, respectively, compared
to an orbital fit of S0-2 alone and a factor of 2.5 compared to previous
results from stellar orbits. This analysis also limits the extended dark mass
within 0.01 pc to less than at 99.7% confidence, a
factor of 3 lower compared to prior work.Comment: 56 pages, 14 figures, accepted to Ap
Widespread Shocks in the Nucleus of NGC 404 Revealed by Near-infrared Integral Field Spectroscopy
We present high spatial resolution, integral field spectrograph (IFS) observations of the nearby low-ionization nuclear emission-line region (LINER) galaxy NGC 404 at 1.25 μm (J band) and 2.2 μm (K band) near-infrared (NIR) wavelengths. Although NGC 404 is thought to host an intermediate-mass black hole (BH) at its center, it has been unclear whether accretion onto the BH or another mechanism such as shock excitation drives its LINER emission at optical/NIR wavelengths. We use the OSIRIS IFS at Keck Observatory behind laser guide star adaptive optics to map the strength and kinematics of [Fe ii], H_2, and hydrogen recombination lines at spatial resolutions of 1 pc across the central 30 pc of the galaxy. The H_2 gas is in a central rotating disk, and ratios of multiple H_2 lines indicate that the molecular gas is thermally excited, with some contribution from UV fluorescence. The [Fe ii] emission is more extended and diffuse than the molecular gas and has a different kinematic structure that reaches higher velocities/dispersions. We also map the strength of the CO stellar absorption feature and constrain the dominant age of the nuclear stellar population to ~1 Gyr. Finally, we find regions across the nucleus of NGC 404 with [Fe ii]/Paβ line ratios up to 6.5, ~2.5 times higher than the ratio measured from spatially integrated spectra. From these high line ratios, we conclude that shocks are the dominant physical mechanism exciting NGC 404's LINER emission and argue that a possible source of this shock excitation is a supernova remnant
Testing the gravitational theory with short-period stars around our Galactic Center
Motion of short-period stars orbiting the supermassive black hole in our
Galactic Center has been monitored for more than 20 years. These observations
are currently offering a new way to test the gravitational theory in an
unexplored regime: in a strong gravitational field, around a supermassive black
hole. In this proceeding, we present three results: (i) a constraint on a
hypothetical fifth force obtained by using 19 years of observations of the two
best measured short-period stars S0-2 and S0-38 ; (ii) an upper limit on the
secular advance of the argument of the periastron for the star S0-2 ; (iii) a
sensitivity analysis showing that the relativistic redshift of S0-2 will be
measured after its closest approach to the black hole in 2018.Comment: 4 pages, 2 figures, proceedings of the 52nd Rencontres de Moriond,
Gravitation Sessio
Keck Observations of the Galactic Center Source G2: Gas Cloud or Star?
We present new observations and analysis of G2—the intriguing red emission-line object which is quickly approaching the Galaxy's central black hole. The observations were obtained with the laser guide star adaptive optics systems on the W. M. Keck I and II telescopes (2006-2012) and include spectroscopy (R ~ 3600) centered on the hydrogen Brγ line as well as K' (2.1 μm) and L' (3.8 μm) imaging. Analysis of these observations shows the Brγ line emission has a positional offset from the L' continuum. This offset is likely due to background source confusion at L'. We therefore present the first orbital solution derived from Brγ line astrometry, which, when coupled with radial velocity measurements, results in a later time of closest approach (2014.21 ± 0.14), closer periastron (130 AU, 1600 R_s), and higher eccentricity (0.9814 ± 0.0060) compared to a solution using L' astrometry. It is shown that G2 has no K' counterpart down to K' ~ 20 mag. G2's L' continuum and the Brγ line emission appears unresolved in almost all epochs, which implies that the bulk of the emission resides in a compact region. The observations altogether suggest that while G2 has a gaseous component that is tidally interacting with the central black hole, there is likely a central star providing the self-gravity necessary to sustain the compact nature of this object
The Post-periapsis Evolution of Galactic Center Source G1: The Second Case of a Resolved Tidal Interaction with a Supermassive Black Hole
We present new adaptive optics (AO) imaging and spectroscopic measurements of Galactic center source G1 from W. M. Keck Observatory. Our goal is to understand its nature and relationship to G2, which is the first example of a spatially resolved object interacting with a supermassive black hole (SMBH). Both objects have been monitored with AO for the past decade (2003–2014) and are comparatively close to the black hole (ɑ_(min) ~ 200–300 au) on very eccentric orbits (ℯ_(G1) ~ 0.99; ℯ_(G2) ~ 0.96). While G2 has been tracked before and during periapsis passage (T_0 ~ 2014.2), G1 has been followed since soon after emerging from periapsis (T_0 ~ 2001.3). Our observations of G1 double the previously reported observational time baseline, which improves its orbital parameter determinations. G1's orbital trajectory appears to be in the same plane as that of G2 but with a significantly different argument of periapsis (Δω = 21° ± 4°). This suggests that G1 is an independent object and not part of a gas stream containing G2, as has been proposed. Furthermore, we show for the first time that (1) G1 is extended in the epochs closest to periapsis along the direction of orbital motion, and (2) it becomes significantly smaller over time (450 au in 2004 to less than 170 au in 2009). Based on these observations, G1 appears to be the second example of an object tidally interacting with an SMBH. G1's existence 14 yr after periapsis, along with its compactness in epochs further from the time of periapsis, suggest that this source is stellar in nature
Detection of Galactic Center Source G2 at 3.8 μm during Periapse Passage
We report new observations of the Galactic Center source G2 from the W. M. Keck Observatory. G2 is a dusty red object associated with gas that shows tidal interactions as it nears its closest approach with the Galaxy's central black hole. Our observations, conducted as G2 passed through periapse, were designed to test the proposal that G2 is a 3 Earth mass gas cloud. Such a cloud should be tidally disrupted during periapse passage. The data were obtained using the Keck II laser guide star adaptive optics system (LGSAO) and the facility near-infrared camera (NIRC2) through the K' [2.1 μm] and L' [3.8 μm] broadband filters. Several results emerge from these observations: (1) G2 has survived its closest approach to the black hole as a compact, unresolved source at L', (2) G2's L' brightness measurements are consistent with those over the last decade, (3) G2's motion continues to be consistent with a Keplerian model. These results rule out G2 as a pure gas cloud and imply that G2 has a central star. This star has a luminosity of ~30 L_☉ and is surrounded by a large (~2.6 AU) optically thick dust shell. The differences between the L' and Br-γ observations can be understood with a model in which L' and Br-γ emission arises primarily from internal and external heating, respectively. We suggest that G2 is a binary star merger product and will ultimately appear similar to the B-stars that are tightly clustered around the black hole (the so-called S-star cluster)
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