ABSTRACT High-Velocity Clouds (HVCs) have been thought to be part of the Galactic accretion proce... more ABSTRACT High-Velocity Clouds (HVCs) have been thought to be part of the Galactic accretion process since their discovery more than 40 years ago. Two modes through which HVCs may be generated and contribute to the ongoing growth of our Galaxy are (1) the tidal stripping of satellite galaxies and (2) the fragmented condensation of the Galaxy's hot baryonic halo. We have run cosmological Tree-SPH simulations of a Milky-Way sized galaxy, in which we can resolve clouds down to 10^5 M&sun;, in an attempt to probe the cooling halo accretion process. The simulations show that this HVC generation mechanism can indeed reproduce the characteristics of observed population of HVCs, including the flux, velocity and cloud clustering properties. These simulations also predict an equally large population of halo clouds moving at lower radial velocities: Low-Velocity Halo Clouds (LVHCs). These clouds would not be observed as HVCs, but would rather be confused with local disk gas. Taking advantage of the known empirical result that HVCs have undetectably low infrared dust flux compared to their 21cm column, we search for these clouds in the preliminary GALFA-HI survey and IRAS. We announce the discovery of the first examples of these clouds, and describe their properties. This work was supported in part by NSF grant AST 04-06987 and NSF grant AST 07-09347.
Berkeley conducts 7 SETI programs at IR, visible and radio wavelengths. Here we review two of the... more Berkeley conducts 7 SETI programs at IR, visible and radio wavelengths. Here we review two of the newest efforts, Astropulse and Fly's Eye. A variety of possible sources of microsecond to millisecond radio pulses have been suggested in the last several decades, among them such exotic events as evaporating primordial black holes, hyper-flares from neutron stars, emissions from cosmic strings
Zenodo (CERN European Organization for Nuclear Research), Jul 6, 2023
The NASA Ionospheric Connection Explorer Extreme Ultraviolet spectrograph, ICON EUV, images onedi... more The NASA Ionospheric Connection Explorer Extreme Ultraviolet spectrograph, ICON EUV, images onedimensional altitude profiles of the daytime EUV airglow between 54-88 nm. This spectral range contains several OII emission features derived from the photoionization of atomic oxygen by solar EUV. The primary target of the ICON EUV is the bright OII (4 P-4 S) triplet emission at 83.4 nm that is used in combination with a dimmer but complementary feature (2 P-2 D) at 61.7 nm that are jointly analyzed to determine the best-fit solution of ionospheric O + density profile between 150-450 km. From this result, the daytime ionospheric F-region peak electron density and height, NmF2 and HmF2 respectively, are inferred. The low-inclination orbit allows measurements across all local times, but also has a precession rate such that low and equatorial latitudes are sampled at all times over a 48-day period. This paper presents observations of the global patterns in ionospheric HmF2 and NmF2 obtained from the first two years of ICON EUV measurements, which occurred during solar minimum conditions, specifically examining longitudinal patterns in these parameters in a fixed local time frame with respect to the persistent longitudinal wave-4 features created by waves in the lower atmosphere.
We describe the pulse detection algorithms used by the most recent versions of SETI@home. The fir... more We describe the pulse detection algorithms used by the most recent versions of SETI@home. The first is a modified folding algorithm with an optimal threshold function. It is designed to efficiently search for repeating pulses over a 15+ octave period range with constant false alarm rate per period searched. This algorithm is potentially useful for other applications where detection of faint pulsed emission is desired (i.e. pulsar searches). The second is a triplet detector which searches for sets of three evenly spaced pulses that exceed a power threshold. It is useful for detecting pulsed emission that has total duration less than the searched exposure. We describe the first results of the use of these algorithms in SETI@home and discuss the pulsed radio frequency interference (RFI) environment of the Arecibo observatory.
ABSTRACT High-Velocity Clouds (HVCs) have been thought to be part of the Galactic accretion proce... more ABSTRACT High-Velocity Clouds (HVCs) have been thought to be part of the Galactic accretion process since their discovery more than 40 years ago. Two modes through which HVCs may be generated and contribute to the ongoing growth of our Galaxy are (1) the tidal stripping of satellite galaxies and (2) the fragmented condensation of the Galaxy's hot baryonic halo. We have run cosmological Tree-SPH simulations of a Milky-Way sized galaxy, in which we can resolve clouds down to 10^5 M&sun;, in an attempt to probe the cooling halo accretion process. The simulations show that this HVC generation mechanism can indeed reproduce the characteristics of observed population of HVCs, including the flux, velocity and cloud clustering properties. These simulations also predict an equally large population of halo clouds moving at lower radial velocities: Low-Velocity Halo Clouds (LVHCs). These clouds would not be observed as HVCs, but would rather be confused with local disk gas. Taking advantage of the known empirical result that HVCs have undetectably low infrared dust flux compared to their 21cm column, we search for these clouds in the preliminary GALFA-HI survey and IRAS. We announce the discovery of the first examples of these clouds, and describe their properties. This work was supported in part by NSF grant AST 04-06987 and NSF grant AST 07-09347.
Berkeley conducts 7 SETI programs at IR, visible and radio wavelengths. Here we review two of the... more Berkeley conducts 7 SETI programs at IR, visible and radio wavelengths. Here we review two of the newest efforts, Astropulse and Fly's Eye. A variety of possible sources of microsecond to millisecond radio pulses have been suggested in the last several decades, among them such exotic events as evaporating primordial black holes, hyper-flares from neutron stars, emissions from cosmic strings
Zenodo (CERN European Organization for Nuclear Research), Jul 6, 2023
The NASA Ionospheric Connection Explorer Extreme Ultraviolet spectrograph, ICON EUV, images onedi... more The NASA Ionospheric Connection Explorer Extreme Ultraviolet spectrograph, ICON EUV, images onedimensional altitude profiles of the daytime EUV airglow between 54-88 nm. This spectral range contains several OII emission features derived from the photoionization of atomic oxygen by solar EUV. The primary target of the ICON EUV is the bright OII (4 P-4 S) triplet emission at 83.4 nm that is used in combination with a dimmer but complementary feature (2 P-2 D) at 61.7 nm that are jointly analyzed to determine the best-fit solution of ionospheric O + density profile between 150-450 km. From this result, the daytime ionospheric F-region peak electron density and height, NmF2 and HmF2 respectively, are inferred. The low-inclination orbit allows measurements across all local times, but also has a precession rate such that low and equatorial latitudes are sampled at all times over a 48-day period. This paper presents observations of the global patterns in ionospheric HmF2 and NmF2 obtained from the first two years of ICON EUV measurements, which occurred during solar minimum conditions, specifically examining longitudinal patterns in these parameters in a fixed local time frame with respect to the persistent longitudinal wave-4 features created by waves in the lower atmosphere.
We describe the pulse detection algorithms used by the most recent versions of SETI@home. The fir... more We describe the pulse detection algorithms used by the most recent versions of SETI@home. The first is a modified folding algorithm with an optimal threshold function. It is designed to efficiently search for repeating pulses over a 15+ octave period range with constant false alarm rate per period searched. This algorithm is potentially useful for other applications where detection of faint pulsed emission is desired (i.e. pulsar searches). The second is a triplet detector which searches for sets of three evenly spaced pulses that exceed a power threshold. It is useful for detecting pulsed emission that has total duration less than the searched exposure. We describe the first results of the use of these algorithms in SETI@home and discuss the pulsed radio frequency interference (RFI) environment of the Arecibo observatory.
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Papers by Eric Korpela