34 research outputs found
Young star clusters in interacting galaxies - NGC 1487 and NGC 4038/4039
We estimate the dynamical masses of several young (~10 Myr) massive star
clusters in two interacting galaxies, NGC 4038/4039 ("The Antennae") and NGC
1487, under the assumption of virial equilibrium. These are compared with
photometric mass estimates from K-band photometry and assuming a standard
Kroupa IMF. The clusters were selected to have near-infrared colors dominated
by red supergiants, and hence to be old enough to have survived the earliest
phases of cluster evolution when the interstellar medium is rapidly swept out
from the cluster, supported by the fact that there is no obvious Halpha
emission associated with the clusters. All but one of the Antennae clusters
have dynamical and photometric mass estimates which are within a factor ~2 of
one another, implying both that standard IMFs provide a good approximation to
the IMF of these clusters, and that there is no significant extra-virial
motion, as would be expected if they were rapidly dispersing. These results
suggest that almost all of the Antennae clusters in our sample have survived
the gas removal phase as bound or marginally bound objects. Two of the three
NGC 1487 clusters studied here have M_dyn estimates which are significantly
larger than the photometric mass estimates. At least one of these two clusters,
and one in the Antennae, may be actively in the process of dissolving. The
process of dissolution contributes a component of non-virial motion to the
integrated velocity measurements, resulting in an estimated M_dyn which is too
high relative to the amount of measured stellar light. The dissolution
candidates in both galaxies are amongst the clusters with the lowest
pressures/densities measured in our sample.Comment: 17 pages, 14 Figures, A&A accepte
The Gemini NICI Planet-Finding Campaign
Our team is carrying out a multi-year observing program to directly image and
characterize young extrasolar planets using the Near-Infrared Coronagraphic
Imager (NICI) on the Gemini-South 8.1-meter telescope. NICI is the first
instrument on a large telescope designed from the outset for high-contrast
imaging, comprising a high-performance curvature adaptive optics system with a
simultaneous dual-channel coronagraphic imager. Combined with state-of-the-art
observing methods and data processing, NICI typically achieves ~2 magnitudes
better contrast compared to previous ground-based or space-based programs, at
separations inside of ~2 arcsec. In preparation for the Campaign, we carried
out efforts to identify previously unrecognized young stars, to rigorously
construct our observing strategy, and to optimize the combination of angular
and spectral differential imaging. The Planet-Finding Campaign is in its second
year, with first-epoch imaging of 174 stars already obtained out of a total
sample of 300 stars. We describe the Campaign's goals, design, implementation,
performance, and preliminary results. The NICI Campaign represents the largest
and most sensitive imaging survey to date for massive (~1 Mjup) planets around
other stars. Upon completion, the Campaign will establish the best measurements
to date on the properties of young gas-giant planets at ~5-10 AU separations.
Finally, Campaign discoveries will be well-suited to long-term orbital
monitoring and detailed spectrophotometric followup with next-generation
planet-finding instruments.Comment: Proceedings of the SPIE, vol 7736 (Advances in Adaptive Optics, San
Diego, CA, June 2010 meeting), in pres
The Gemini NICI Planet-Finding Campaign: The Frequency of Giant Planets Around Debris Disk Stars
We have completed a high-contrast direct imaging survey for giant planets
around 57 debris disk stars as part of the Gemini NICI Planet-Finding Campaign.
We achieved median H-band contrasts of 12.4 mag at 0.5" and 14.1 mag at 1"
separation. Follow-up observations of the 66 candidates with projected
separation < 500 AU show that all of them are background objects. To establish
statistical constraints on the underlying giant planet population based on our
imaging data, we have developed a new Bayesian formalism that incorporates (1)
non-detections, (2) single-epoch candidates, (3) astrometric and (4)
photometric information, and (5) the possibility of multiple planets per star
to constrain the planet population. Our formalism allows us to include in our
analysis the previously known Beta Pictoris and the HR 8799 planets. Our
results show at 95% confidence that 5MJup
planet beyond 80 AU, and 3MJup planet outside
of 40 AU, based on hot-start evolutionary models. We model the population of
directly-imaged planets as d^2N/dMda ~ m^alpha a^beta, where m is planet mass
and a is orbital semi-major axis (with a maximum value of amax). We find that
beta 1.7. Likewise, we find that beta < -0.8 and/or amax
< 200 AU. If we ignore the Beta Pic and HR 8799 planets (should they belong to
a rare and distinct group), we find that
3MJup planet beyond 10 AU, and beta < -0.8 and/or alpha < -1.5. Our Bayesian
constraints are not strong enough to reveal any dependence of the planet
frequency on stellar host mass. Studies of transition disks have suggested that
about 20% of stars are undergoing planet formation; our non-detections at large
separations show that planets with orbital separation > 40 AU and planet masses
> 3 MJup do not carve the central holes in these disks.Comment: Accepted to ApJ on June 24, 2013. 67 pages, 17 figures, 12 table
The E-ELT first light spectrograph HARMONI: capabilities and modes
Trabajo presentado en SPIE Astronomical Telescopes, celebrado en San Diego (California), del 26 de junio al 1 de julio de 2016HARMONI is the E-ELT's first light visible and near-infrared integral field spectrograph. It will provide four different spatial scales, ranging from coarse spaxels of 60 × 30 mas best suited for seeing limited observations, to 4 mas spaxels that Nyquist sample the diffraction limited point spread function of the E-ELT at near-infrared wavelengths. Each spaxel scale may be combined with eleven spectral settings, that provide a range of spectral resolving powers (R 3500, 7500 and 20000) and instantaneous wavelength coverage spanning the 0.5 - 2.4 ¿m wavelength range of the instrument. In autumn 2015, the HARMONI project started the Preliminary Design Phase, following signature of the contract to design, build, test and commission the instrument, signed between the European Southern Observatory and the UK Science and Technology Facilities Council. Crucially, the contract also includes the preliminary design of the HARMONI Laser Tomographic Adaptive Optics system. The instrument's technical specifications were finalized in the period leading up to contract signature. In this paper, we report on the first activity carried out during preliminary design, defining the baseline architecture for the system, and the trade-off studies leading up to the choice of baseline
Dynamical masses of young star clusters in interacting galaxies
Using ISAAC on VLT-ANTU and UVES on VLT-KUEYEN we have begun a program to measure stellar velocity dispersions of young star clusters in merging and interacting galaxies. In this contribution, we present results for clusters in two interacting galaxies - NGC 4038/39 and NGC 1487. Combining the measured velocity dispersions with sizes of the clusters estimated from Hubble Space Telescope imaging data resulted in the first determinations of dynamical masses of stellar clusters in galaxy mergers. Due to the faintness of the clusters and the high spectral resolution required, these results could only be obtained in with 10m class telescopes. Our results suggest that masses, sizes and concentrations of the light distributions are comparable to those of globular clusters, supporting the idea that part of the globular cluster population in elliptical galaxies is formed as a result of a merger event between to gas-rich spiral galaxies. However, the initial mass function (IMF) of the stars in the clusters seems to vary with environment: In some regions (dust-rich?), the IMF is more biased towards low-mass stars than in other (dust-poor) regions. There is a long-standing and substantial controversy in the literature whether or not their exists a "universal IMF". Our results for clusters in merging galaxies support the notion that the IMF depends on the birth environment of the cluster or perhaps some other variable. The relative content of low mass stars also influences the survival probability of stellar clusters. For their masses and light concentrations, some of the clusters have sufficiently shallow IMFs that it is likely that they will dissolve within a Hubble time, while for others, the IMF is sufficiently steep that they are likely to survive but undergo significant mass loss during their evolution
Young star clusters in the Antennae galaxies and NGC 1487
International audienceWe estimate the dynamical masses of several young ({≈ 10} Myr) massive star clusters in two interacting galaxies, NGC 4038/4039 (``The Antennae") and NGC 1487, under the assumption of virial equilibrium. These are compared with photometric mass estimates. A dynamical mass substantially higher than the photometric estimate could indicate non-virial motion of the stars in the cluster, and potentially lead to cluster disruption. All but one of the Antennae clusters have dynamical and photometric mass estimates which are within a factor ≈ 2 of one another, implying both that standard IMFs provide a good approximation to the IMF of these clusters, and that there is no significant extra-virial motion, as would be expected if they were rapidly dispersing. These results suggest that almost all of the clusters in our sample have survived the gas removal phase as bound or marginally bound objects. But a few targets (two in NGC 1487 and one in the Antennae) have M_dyn estimates which are significantly larger than the photometric mass estimates. At least two of those clusters may be actively in the process of dissolving. The dissolution candidates in both galaxies are amongst the clusters with the lowest pressures/densities measured in our sample
Simulating gas kinematic studies of high-redshift galaxies with the HARMONI integral field spectrograph
We present simulated observations of gas kinematics in a galaxy formed in a 10 pc resolution cosmological simulation with the hydrodynamical + N-body code ramses, using the new ramses2hsim pipeline with the simulated observing pipeline (hsim) for the Extremely Large Telescope High Angular Resolution Monolithic Optical and Near-infrared Integral field spectrograph (HARMONI IFS). We post-process the galaxy's gas kinematics and Hα line emission for each simulation cell, and integrate the emission to produce an extinction-corrected input cube. We then simulate observations of the input cube with HARMONI, for a range of exposure times, spatial sampling, and spectral resolution. We analyse the mock observations to recover galaxy properties such as its kinematics and compare with the known simulation values. We investigate the cause of biases between the 'real' and 'observed' kinematic values, demonstrating the sensitivity of the inferred rotation curve to knowledge of the instrument's point spread function