ABSTRACT 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 2 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 yr) 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 (Mbh) and distance (Ro) of Sgr A*: Mbh = (4.02 0.16 0.04) × 106 M and 7.86 0.14 0.04 kpc. The uncertainties in Mbh and Ro 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 0.13 × 106 M at 99.7% confidence, a factor of 3 lower compared to prior work.
We demonstrate that short-period stars orbiting around the supermassive black hole in our Galactic center can successfully be used to probe the gravitational theory in a strong regime. We use ...19 years of observations of the two best measured short-period stars orbiting our Galactic center to constrain a hypothetical fifth force that arises in various scenarios motivated by the development of a unification theory or in some models of dark matter and dark energy. No deviation from general relativity is reported and the fifth force strength is restricted to an upper 95% confidence limit of |α|<0.016 at a length scale of λ=150 astronomical units. We also derive a 95% confidence upper limit on a linear drift of the argument of periastron of the short-period star S0-2 of |ωover ˙_{S0-2}|<1.6×10^{-3} rad/yr, which can be used to constrain various gravitational and astrophysical theories. This analysis provides the first fully self-consistent test of the gravitational theory using orbital dynamic in a strong gravitational regime, that of a supermassive black hole. A sensitivity analysis for future measurements is also presented.
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 Br? line as well as K' (2.1 mu m) and L' (3.8 mu m) imaging. Analysis of these observations shows the Br? 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 Br gamma line astrometry, which, when coupled with radial velocity measurements, results in a later time of closest approach (2014.21 + or - 0.14), closer periastron (130 AU, 1600 R sub(s)), and higher eccentricity (0.9814+ or -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 Br gamma 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.
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 mu m and L' 3.8 mu m 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 sub(middot in circle) and is surrounded by a large (~2.6 AU) optically thick dust shell. The differences between the L' and Br- gamma observations can be understood with a model in which L' and Br- gamma 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).
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 m (J band) and 2.2 m (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, H2, and hydrogen recombination lines at spatial resolutions of 1 pc across the central 30 pc of the galaxy. The H2 gas is in a central rotating disk, and ratios of multiple H2 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.
Context. Nearby stars are prime targets for exoplanet searches and characterization using a variety of detection techniques. Combining constraints from the complementary detection methods of ...high-contrast imaging (HCI) and radial velocity (RV) can further constrain the planetary architectures of these systems because these methods place limits at different regions of the companion mass and semi-major axis parameter space. Compiling a census of the planet population in the solar neighborhood is important to inform target lists for future space missions that will specifically target nearby stars to search for Earth analogs. Aims. We aim to constrain the planetary architectures from the combination of HCI and RV data for six nearby stars within 6 pc: τ Ceti, Kapteyn’s star, AX Mic, 40 Eri, HD 36395, and HD 42581. We explored where HCI adds information to constraints from the long-term RV monitoring data for these stars. Methods. We compiled the sample from stars with available archival VLT/NACO HCI data at L′ band (3.8 μm), where we expect substellar companions to be brighter for the typically older ages of nearby field stars (>1 Gyr). The NACO data were fully reanalyzed using the state-of-the-art direct imaging pipeline PynPoint and combined with RV data from HARPS, Keck/HIRES, and CORALIE. A Monte Carlo approach was used to assess the completeness in the companion mass and semi-major axis parameter space from the combination of the HCI and RV data sets. Results. We find that the HCI data add significant information to the RV constraints, increasing the completeness for certain companions masses and semi-major axes by up to 68–99% for four of the six stars in our sample, and by up to 1–13% for the remaining stars. The improvements are strongest for intermediate semi-major axes (15–40 AU), corresponding to the semi-major axes of the ice giants in our own solar system. The HCI mass limits reach 5–20 MJup in the background-limited regime, depending on the age of the star. Conclusions. Through the combination of HCI and RV data, we find that stringent constraints can be placed on the possible substellar companions in these systems. Applying these methods systematically to nearby stars will quantify our current knowledge of the planet population in the solar neighborhood and inform future observations.
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 (amin ∼ 200-300 au) on very eccentric orbits (eG1 ∼ 0.99; eG2 ∼ 0.96). While G2 has been tracked before and during periapsis passage (T0 ∼ 2014.2), G1 has been followed since soon after emerging from periapsis (T0 ∼ 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 (Δ = 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.
Context.
The direct imaging of rocky exoplanets is one of the major science goals of upcoming large telescopes. The contrast requirement for imaging such planets is challenging. However, the mid-IR ...(infrared) regime provides the optimum contrast to directly detect the thermal signatures of exoplanets in our solar neighbourhood.
Aims.
We aim to exploit novel fast-chopping techniques newly developed for astronomy with the aid of adaptive optics to look for thermal signatures of exoplanets around bright stars in the solar neighbourhood.
Methods.
We used the upgraded Very Large Telescope Imager and Spectrometer for the mid-InfraRed (VISIR) instrument with high-contrast imaging capability optimised for observations at 10 μm to look for exoplanets around five nearby (
d
< 4 pc) stars. The instrument provides an improved signal-to-noise ratio (S/N) by a factor of ~4 in the
N
-band compared to standard VISIR for a given S/N and time.
Results.
In this work, we achieve a detection sensitivity of sub-mJy, which is sufficient to detect a few Jupiter mass planets in nearby systems. Although no detections are made, we achieve most sensitive limits within <2″ for all the observed targets compared to previous campaigns. For
ϵ
Indi A and
ϵ
Eri, we achieve detection limits very close to the giant planets discovered by RV, with the limits on
ϵ
Indi A being the most sensitive to date. Our non-detection therefore supports an older age for
ϵ
Indi A. The results presented here are promising for high-contrast imaging and exoplanet detections in the mid-IR regime.
Molecular mapping of the PDS70 system Cugno, G; Patapis, P; Stolker, T ...
Astronomy and astrophysics (Berlin),
09/2021, Letnik:
653
Journal Article
Recenzirano
Odprti dostop
Context. Determining the chemical properties of the atmosphere of young forming gas giants might shed light on the location their formation occurred and the mechanisms involved. Aims. Our aim was to ...detect molecules in the atmosphere of the young forming companion PDS70 b by searching for atmospheric absorption features typical of substellar objects. Methods. We obtained medium-resolution (R ≈ 5075) spectra of the PDS70 planetary system with the SINFONI integral field spectrograph at the Very Large Telescope. We applied molecular mapping, based on cross-correlation with synthetic spectra, to identify signatures of molecular species in the atmosphere of the planet. Results. Although the planet emission is clearly detected when resampling the data to lower resolution, no molecular species could be identified with the cross-correlation technique. We estimated upper limits on the abundances of H2O, CO, and CH4 (log(Xmol) < −4.0, − 4.1, and − 4.9, respectively) assuming a clear atmosphere, and we explored the impact of clouds, which increase the upper limits by a factor of up to 0.7 dex. Assuming that the observations directly probe the planet’s atmosphere, we found a lack of molecular species compared to other directly imaged companions or field objects. Under the assumption that the planet atmosphere presents similar characteristics to other directly imaged planets, we conclude that a dusty environment surrounds the planet, effectively obscuring any feature generated in its atmosphere. We quantify the extinction necessary to impede the detection (AV ≈ 16−17 mag), pointing to the possibility of higher optical thickness than previously estimated from other studies. Finally, the non-detection of molecular species conflicts with atmospheric models previously proposed to describe the forming planet. Conclusions. To reveal how giant planets form a comprehensive approach that includes constraints from multiple techniques needs to be undertaken. Molecular mapping emerges as an alternative to more classical techniques like SED fitting. Specifically tuned atmospheric models are likely required to faithfully describe the atmospheres of forming protoplanets, and higher spectral resolution data may reveal molecular absorption lines despite the dusty environment enshrouding PDS70 b.
Purpose
To analyze outcomes and complication rates in an unselected cohort of men with unfavorable (NCCN intermediate and high-risk) PCa receiving combined-modality radiation treatment (CRT).
Methods
...Patients received androgen deprivation therapy for 1 year and combined-modality radiation treatment (CRT) consisting of external-beam radiotherapy (EBRT, 59.4 Gy, 33 fractions) and
125
J seed-brachytherapy (S-BT, 100 Gy). Subgroups, including WHO group 3–5, and initial PSA (iPSA) < 20 and > 20 ng/ml were identified. Biochemical recurrence-free (BRFS), metastasis-free (MFS), cancer-specific (CSS) and overall survival (OS) were calculated at 5 and 10 years using the Kaplan–Meier method. Subgroups were compared using log-rank test and Cox proportional hazards regression. Urogenital and gastrointestinal side-effects were reported according to the CTCAE classification.
Results
After a median of 6.9 years (range 2–13) calculated 5- and 10-year rates for the whole cohort of 425 men were 92.8% and 82.5% for BRFS, 95.1%, and 88.8% for MFS, 98.2%, and 95.1 for CSS, and 95.4%, and 80.1% for OS, respectively. Univariate (UVA) and multivariate analysis (MV) identified a group with unfavorable outcome with iPSA > 20 ng/ml, comprising 24% of all patients, in which 55% of recurrences, 54% of metastases and 71% of cancer-specific deaths occurred. Side-effects were limited, with < 5% of patients complaining of genitourinary and 0.5% of gastrointestinal AEs after 5 years.
Conclusion
CRT is an excellent treatment option for men with unfavorable PCa. In a subgroup of patients with iPSA > 20 ng/ml further, possibly systemic, treatment options should be identified.
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