150 research outputs found
Constraining the Physical Properties of Meteor Stream Particles by Light Curve Shapes Using the Virtual Meteor Observatory
Different authors have produced models for the physical properties of meteoroids based on the shape of a meteor's light curve, typically from short observing campaigns. We here analyze the height profiles and light curves of approx.200 double-station meteors from the Leonids and Perseids using data from the Virtual Meteor Observatory, to demonstrate that with this web-based meteor database it is possible to analyze very large datasets from different authors in a consistent way. We compute the average heights for begin point, maximum luminosity, and end heights for Perseids and Leonids. We also compute the skew of the light curve, usually called the F-parameter. The results compare well with other author's data. We display the average light curve in a novel way to assess the light curve shape in addition to using the F-parameter. While the Perseids show a peaked light curve, the average Leonid light curve has a more flat peak. This indicates that the particle distribution of Leonid meteors can be described by a Gaussian distribution; the Perseids can be described with a power law. The skew for Leonids is smaller than for Perseids, indicating that the Leonids are more fragile than the Perseids
Calibrated and completeness-corrected optical stellar density maps of the Northern Galactic Plane
© The Author 2016. Published by Oxford University Press on behalf of The Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.Following on from the second release of calibrated photometry from IPHAS, the INT/WFC Photometric Hα Survey of the Northern Galactic Plane, we present incompleteness-corrected stellar density maps in the r and i photometric bands. These have been computed to a range of limiting magnitudes reaching to 20th magnitude in r and 19th in i (Vega system), and with different angular resolutions – the highest resolution available being 1 arcmin2. The maps obtained cover 94 per cent of the 1800 square degree IPHAS footprint, spanning the Galactic latitude range, −5◦ < b < +5◦, north of the celestial equator. The corrections for incompleteness, due to confusion and sensitivity loss at the faint limit, have been deduced by the method of artificial source injection. The presentation of this method is preceded by a discussion of other more approximate methods of determining completeness. Our method takes full account of position-dependent seeing and source ellipticity in the survey data base. The application of the star counts to testing reddened Galactic disc models is previewed by a comparison with predicted counts along three constant-longitude cuts at 30◦, 90◦ and 175◦: some overprediction of the most heavily reddened 30◦ counts is found, alongside good agreement at 90◦ and 175◦. KeyPeer reviewedFinal Published versio
Galactic Plane H Surveys: IPHAS & VPHAS+
The optical Galactic Plane H surveys IPHAS and VPHAS+ are
dramatically improving our understanding of Galactic stellar populations and
stellar evolution by providing large samples of stars in short lived, but
important, evolutionary phases, and high quality homogeneous photometry and
images over the entire Galactic Plane. Here I summarise some of the
contributions these surveys have already made to our understanding of a number
of key areas of stellar and Galactic astronomy.Comment: 5 pages, 2 figures, refereed proceeding of the "The Universe of
Digital Sky Surveys" conference, November 2014, to be published in the
Astrophysics and Space Science Proceeding
A 3D extinction map of the northern Galactic plane based on IPHAS photometry
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. ©: 2014 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.We present a 3D map of extinction in the northern Galactic plane derived using photometry from the INT/WFC Photometric Hα Survey of the northern Galactic plane. The map has fine angular (~10 arcmin) and distance (100 pc) sampling allied to a significant depth (≳5 kpc). We construct the map using a method based on a hierarchical Bayesian model described in a previous article by Sale. In addition to mean extinction, we also measure differential extinction, which arises from the fractal nature of the interstellar medium, and show that it will be the dominant source of uncertainty in estimates of extinction to some arbitrary position. The method applied also furnishes us with photometric estimates of the distance, extinction, effective temperature, surface gravity, and mass for ~38 million stars. Both the extinction map and the catalogue of stellar parameters are made publicly available via http://www.iphas.org/extinction.Peer reviewe
Photometry of K2 Campaign 9 bulge data
In its Campaign 9, K2 observed dense regions toward the Galactic bulge in
order to constrain the microlensing parallaxes and probe for free-floating
planets. Photometric reduction of the \emph{K2} bulge data poses a significant
challenge due to a combination of the very high stellar density, large pixels
of the Kepler camera, and the pointing drift of the spacecraft. Here we present
a new method to extract K2 photometry in dense stellar regions. We extended the
Causal Pixel Model developed for less-crowded fields, first by using the pixel
response function together with accurate astrometric grids, second by combining
signals from a few pixels, and third by simultaneously fitting for an
astrophysical model. We tested the method on two microlensing events and a
long-period eclipsing binary. The extracted K2 photometry is an order of
magnitude more precise than the photometry from other method
The ionized nebula surrounding the red supergiant W26 in Westerlund 1
We present Hα images of an ionized nebula surrounding the M2-5Ia red supergiant (RSG) W26 in the massive star cluster Westerlund 1. The nebula consists of a circumstellar shell or ring ∼0.1 pc in diameter and a triangular nebula ∼0.2 pc from the star that in high-resolution Hubble Space Telescope images shows a complex filamentary structure. The excitation mechanism of both regions is unclear since RSGs are too cool to produce ionizing photons and we consider various possibilities. The presence of the nebula, high stellar luminosity and spectral variability suggests that W26 is a highly evolved RSG experiencing extreme levels of mass-loss. As the only known example of an ionized nebula surrounding an RSG W26 deserves further attention to improve our understanding of the final evolutionary stages of massive stars
The Gaia-ESO Survey: Chromospheric Emission, Accretion Properties, and Rotation in Velorum and Chamaeleon I
We use the fundamental parameters delivered by the GES consortium in the
first internal data release to select the members of Vel and Cha I
among the UVES and GIRAFFE spectroscopic observations. A total of 140
Vel members and 74 Cha I members were studied. We calculated stellar
luminosities through spectral energy distributions, while stellar masses were
derived by comparison with evolutionary tracks. The spectral subtraction of
low-activity and slowly rotating templates, which are rotationally broadened to
match the of the targets, enabled us to measure the equivalent widths
(EWs) and the fluxes in the H and H lines. The H line
was also used for identifying accreting objects and for evaluating the mass
accretion rate (). The distribution of for the
members of Vel displays a peak at about 10 km s with a tail
toward faster rotators. There is also some indication of a different
distribution for the members of its two kinematical populations. Only a handful
of stars in Vel display signatures of accretion, while many more
accretors were detected in the younger Cha~I. Accreting and active stars occupy
two different regions in a -flux diagram and we propose a
criterion for distinguishing them. We derive in the ranges
-yr and -yr
for Vel and Cha I accretors, respectively. We find less scatter in the
relation derived through the H EWs, when
compared to the H diagnostics, in agreement with other authors
Classical T Tauri stars with VPHAS+ -I : H α and u-band accretion rates in the Lagoon Nebula M8
We estimate the accretion rates of 235 Classical T Tauri star (CTTS) candidates in the Lagoon Nebula using H photometry from the VPHAS+ survey. Our sample consists of stars displaying H-excess, the intensity of which is used to derive accretion rates. For a subset of 87 stars, the intensity of the -band excess is also used to estimate accretion rates. We find the mean variation in accretion rates measured using H and -band intensities to be 0.17 dex, agreeing with previous estimates (0.04-0.4 dex) but for a much larger sample. The spatial distribution of CTTS align with the location of protostars and molecular gas suggesting that they retain an imprint of the natal gas fragmentation process. Strong accretors are concentrated spatially, while weak accretors are more distributed. Our results do not support the sequential star forming processes suggested in the literature.Peer reviewe
K2: Background Survey - The search for undiscovered transients in Kepler/K2 data
The K2 mission of the Kepler Space Telescope offers a unique possibility to examine sources of both Galactic and extragalactic origin with high-cadence photometry. Alongside the multitude of supernovae and quasars detected within targeted galaxies, it is likely that Kepler has serendipitously observed many transients throughout K2. Such events will likely have occurred in background pixels, coincidentally surrounding science targets. Analysing the background pixels presents the possibility to conduct a high-cadence survey with areas of a few square degrees per campaign. We demonstrate the capacity to independently recover key K2 transients such as KSN 2015K and SN 2018oh. With this survey, we expect to detect numerous transients and determine the first comprehensive rates for transients with lifetimes of <1 d.This research was supported by an Australian Government
Research Training Program (RTP) Scholarship and utilizes data
collected by the K2 missio
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