462 research outputs found
Observing Exoplanets in the Near-Infrared from a High Altitude Balloon Platform
No full textAlthough there exists a large sample of known exoplanets, little data exists that can be used to study their global atmospheric properties. This deficiency can be addressed by performing phase-resolved spectroscopy - continuous spectroscopic observations of a planet's entire orbit about its host star - of transiting exoplanets. Planets with characteristics suitable for atmospheric characterization have orbits of several days, thus phase curve observations are highly resource intensive, especially for shared use facilities. In this work, we show that an infrared spectrograph operating from a high altitude balloon platform can perform phase-resolved spectroscopy of hot Jupiter-type exoplanets with performance comparable to a space-based telescope. Using the EXoplanet Climate Infrared TElescope (EXCITE) experiment as an example, we quantify the impact of the most important systematic effects that we expect to encounter from a balloon platform. We show an instrument like EXCITE will have the stability and sensitivity to significantly advance our understanding of exoplanet atmospheres. Such an instrument will both complement and serve as a critical bridge between current and future space-based near-infrared spectroscopic instruments
Mapping Submillimetre Polarization with BLASTPol
No full textBLASTPol observes the linearly polarized emission from interstellar dust. Dust polarization traces magnetic fields, and submillimetre wavelengths can see into the dense molecular clouds in which stars are born. With this measurement, BLASTPol can help resolve long-standing questions about the role of magnetic fields in the beginning of star formation.BLASTPol is a 1.8 m telescope with 288 Herschel/SPIRE-heritage bolometric detectors at 250 μm, 350 μm, and 500 μm. Polarimetric capability was added with photolithographed grids and a stepped half-wave plate. This work outlines the instrument, with a focus on the BLASTbus electronics system for detector readout, telescope attitude control, and cryogenic housekeeping.In December 2010 and in December 2012, BLASTPol had two long duration balloon flights. An improved map making procedure has been used for reducing the 2012 dataset to maps of the polarized sky. The overall data analysis procedure is described, along with details of the map maker characterization. Finally, maps are presented for the seven targets observed during the 2012 flight. The 14 square degree map of the Vela~C giant molecular cloud is of particularly high quality and will be used in several upcoming studies of dust physics and star formation.Ph.D
Mapping Submillimetre Polarization with BLASTPol
No full textBLASTPol observes the linearly polarized emission from interstellar dust. Dust polarization traces magnetic fields, and submillimetre wavelengths can see into the dense molecular clouds in which stars are born. With this measurement, BLASTPol can help resolve long-standing questions about the role of magnetic fields in the beginning of star formation.BLASTPol is a 1.8 m telescope with 288 Herschel/SPIRE-heritage bolometric detectors at 250 μm, 350 μm, and 500 μm. Polarimetric capability was added with photolithographed grids and a stepped half-wave plate. This work outlines the instrument, with a focus on the BLASTbus electronics system for detector readout, telescope attitude control, and cryogenic housekeeping.In December 2010 and in December 2012, BLASTPol had two long duration balloon flights. An improved map making procedure has been used for reducing the 2012 dataset to maps of the polarized sky. The overall data analysis procedure is described, along with details of the map maker characterization. Finally, maps are presented for the seven targets observed during the 2012 flight. The 14 square degree map of the Vela~C giant molecular cloud is of particularly high quality and will be used in several upcoming studies of dust physics and star formation.Ph.D
The inner structure of ACDM halos
No full textWe have used high resolution N-body simulations to investigate the internal properties of Cold Dark Matter (CDM) halos with virial masses of M(_200) ~ 10(^10) M(_o) at z = 0, comparable to those of dwarf galaxy halos, forming in the ACDM cosmology. In particular, we have focused on providing accurate constraints on the mass distribution in these objects at ~ 1% of the virial radius, r(_200)-. After a brief introduction (chapter 1), the first part of this thesis is concerned with establishing the conditions under which the distribution of mass in simulated CDM halos is unaffected by finite numerical resolution. In chapter 2, we present results from a comprehensive set of simulations of a single galaxy mass halo in which numerical parameters have been varied systematically in order to determine their impact on the spherically averaged mass profile. Based on these results, we have defined a set of convergence criteria that allow us to identify the radial extent over which the spherically averaged circular velocity profile can be considered reliably resolved to better than 10%. In chapter 3, we have examined the abundance of substructure found in three sets of "converged" simulations, and quantified the effect of increasing mass resolution on the number of resolved subhalos of a given mass. The second part of this thesis is concerned with the detailed analysis of the internal structure and kinematics of the simulated dwarf galaxy halos in our sample. In chapter 4, we analyse the structure and kinematics of the dwarfs for possible redshift dependence, and investigate whether these halos could sustain a gaseous disk. In chapter 5, we concentrate on mass dependent trends by performing a detailed comparison with galaxy and cluster mass halos. Finally, chapter 6 provides a summary of the main findings of this work and highlights aspects that may prove rewarding for further study
High-latitude galactic dust emission in the BOOMERANG maps
No full textWe present millimeter-wave observations obtained by the BOOMERANG (Balloon Observations Of Millimetric Extragalactic Radiation ANd Geophysics) experiment of Galactic emission at intermediate and high (b ) Galactic latitudes. We find that this emission is well correlated with extrapolated dust maps and is spectrally consistent with thermal emission from interstellar dust (ISD). The ISD brightness in the 410 GHz map has an angular power spectrum c(l) similar to l(-beta) with 2 less than or similar to beta less than or similar to 3. At 150 GHz and at multipoles l similar to 200, the angular power spectrum of the IRAS- correlated dust signal is estimated to be l/(l + 1)c(l)/2 pi = 3.7 +/- 2.9 muK(2). This is negligible with respect to the cosmic microwave background (CMB) signal measured by the same experiment l(l + 1)c(l)/2 pi = 4700 +/- 540 muK(2). For the uncorrelated dust signal, we set an upper limit to the contribution to the CMB power at 150 GHz and of l similar to 200 l(l + l)c(l)/2 pi K-2 at 95% CL
SPIDER optimization: probing the systematics of a large scale B-mode experiment
No full textSpider is a long-duration, balloon-borne polarimeter designed to measure large-scale cosmic microwave background
(CMB) polarization with very high sensitivity and control of systematics. The instrument will map over half the sky
with degree angular resolution in the I, Q, and U Stokes parameters in four frequency bands from 96 to 275 GHz.
Spider’s ultimate goal is to detect the primordial gravity-wave signal imprinted on the CMB B-mode polarization.
One of the challenges in achieving this goal is the minimization of the contamination of B-modes by systematic effects.
This paper explores a number of instrument systematics and observing strategies in order to optimize B-mode sensitivity.
This is done by injecting realistic-amplitude, time-varying systematics into a set of simulated time streams.
Tests of the impact of detector noise characteristics, pointing jitter, payload pendulations, polarization angle offsets,
beam systematics, and receiver gain drifts are shown. Spider’s default observing strategy is to spin continuously in
azimuth, with polarization modulation achieved by either a rapidly spinning half-wave plate or a rapidly spinning gondola
and a slowly stepped half-wave plate. Although the latter is more susceptible to systematics, the results shown
here indicate that either mode of operation can be used by Spider
Probing Interstellar Grain Alignment with Balloon-borne Submillimeter Observations
No full textThe role that magnetic fields play in regulating star formation is one of the outstanding issues in star formation theory. Magnetic fields in star-forming clouds in our galaxy can be observed by tracing the polarized emission from interstellar dust grains. However the mechanism by which the dust grains align with the magnetic fields is not fully understood. Grain alignment theories (e.g. radiative alignment torques) make predictions for the observed spectrum of the polarized emission, so observations at multiple wavelengths can be used to test these theories. The Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry (BLASTPol) observes polarized dust at 250um, 350um and 500um while suspended from a balloon in the stratosphere above Antarctica. BLASTPol maps the dust polarization signal over entire molecular clouds, with enough angular resolution to trace the cloud sub-structures and protostellar cores. BLASTPol uses an attitude reconstruction system consisting of multiple sensors, including star cameras, sun sensors and rate gyroscopes. This system allows BLASTPol to point in-flight at specific regions on the sky, and allows the telescope’s attitude to be reconstructed post-flight. A similar system was built for SPIDER, a balloon-borne telescope that observes the polarization of the CMB.
The analysis pipeline used to produce science maps is discussed, and science results are presented from BLASTPol’s 2012 observations of the Vela C molecular cloud. The polarization spectrum shows a minimum at 350um, similar to the measurements of previous experiments observing other molecular clouds. No strong correlation is seen between he shape of the polarization spectrum and either the temperature or density of the dust. Analysis of the maps is ongoing, and future work will focus on the diffuse dust in the cloud, which is more suitable to compare with dust models.Ph.D
Probing primordial non Gaussianity in the BOOMERanG CMB maps: an analysis based on analytical Minkowski functionals
No full textMinkowski functionals are a powerful tool to constrain the Gaussianity of the Cosmic Microwave Background (CMB). In the limit of a weakly non Gaussian field, a perturbative approach can be derived [Hikage C., Komatsu E., & Matsubara T., 2006, ApJ, 653, 11] that is completely based on analytical formulae without requiring computationally intensive, dedicated Monte Carlo non Gaussian simulations of the CMB anisotropy. We apply this machinery to an intensity map derived from the 1998 and 2003 flights of BOOMERanG, analyzed here together for the first time. We set limits on the non-linear coupling parameter fNL as −1020<fNL<390 at 95% CL, markedly improving the previous constraints set by [De Troia G. et al., 2007, ApJ, 670, L73] whose analysis was limited to the BOOMERanG 2003 dataset. These limits are the most stringent ever set among suborbital experiments
A measurement by BOOMERANG of multiple peaks in the angular power spectrum of the cosmic microwave background
No full textThis paper presents a measurement of the angular power spectrum of the cosmic microwave background from l = 75 to l = 1025 (similar to10' to 2.degrees4) from a combined analysis of four 150 GHz channels in the BOOMERANG experiment. The spectrum contains multiple peaks and minima, as predicted by standard adiabatic inflationary models in which the primordial plasma undergoes acoustic oscillations. These results, in concert with other types of cosmological measurements and theoretical models, significantly constrain the values of Omega(tot), Omega(b)h(2), Omega(c)h(2), and n(s)
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