1,721,048 research outputs found
Photometry of the UWISH2 extended H2 source catalogue
Full text linkThe UKIRT Widefield Infrared Survey for H2 (UWISH2) is a large, unbiased survey of extended H2 emission sources, using the 1-0 S(1) emission line at 2.122?m. It covers 209 square degrees of the Galactic Plane (GP) between l ? 357° to l ? 66° and b ? ±1.5°. UWISH2 further covers high column density regions in Cygnus and Auriga, covering approximately 42 and 35.5 square degrees respectively and leading to a total survey coverage of ? 286.5 square degrees. As part of the UWISH2 team, I have performed the photometry for 33200 individual H2 features, which have been found to compose ~ 700 H2 jets and outflows, 284 planetary nebulae (PNe), 30 supernova remnants (SNRs) and ~ 1300 photo-dissociation regions (PDRs). About 60% of PNe are newly discovered candidates. Using H2 emission as a tracer for star formation, I find that the majority of H2 flux is located in the lower Galactic longitudes for jet and PDR features, indicating increased star formation activity. I have also observed partial concentrations of high H2 flux at higher Galactic longitudes in the GP from jet features but not PDR features, indicating a lack of high-mass star formation at this region. I offer two methods of photometry: the 'total flux' photometry and the 'median surface brightness times area' photometry. Upon comparing the ratios of the fluxes from both photometries for each feature, I find good agreement (full catalogue: ~ 97% in a 100% deviation and ~ 82% in a 20% deviation) for all feature classes except jets, and recommend the median surface brightness times area photometry for all feature types except jets, which should use total flux photometry. Finally, I have calculated the signal-to-noise ratios for individual features, finding the median value for the entire survey to be approximately 15 when using the feature area
A Study of Light-curves of Nearby Dipper YSOs to Determine Circumstellar Disk Properties
Full text linkThe magnitudes of nearby young stellar objects, recorded in three filters (visual, red, and infra-red), have been observed by the Beacon Observatory since September 2015. Using the data up until November 2017, the light-curves of the objects were studied for the presence of dipper stars. The long term changes in magnitude were taken into account when searching for short dips caused by increased density of material along the line of sight in the inner disk. The depth and duration of these dips were observed and used alongside basic assumptions of stellar mass and distance from the star to estimate the mass and dimensions of material clumps in the inner disk. This was done so as to better understand the evolution of young stars, and the structure of accretion disks. The parameters of the dips found were consistent with previous work on the topic, and provide the starting blocks to produce a structural model of the inner disks of young stars
Long-Term Time-Series Photometry in Cygnus
Full text linkIn this thesis we present the data reduction, database creation and photometric correction of a large, high cadence data-set provided by an amateur astronomer. We also discuss the potential science projects available from this data. The database and catalogue produced via the methods detailed in this report feature 19,858 stars within a 2.8 x 2.8 degree square centred on 317.0, +46.5 (J2000). Each star has ~ 64,000 measurements collected between 2003-09 to 2009-09. The final, photometrically corrected magnitudes have an approximate error of +/0 0.025 mag for bright stars and+/-0.040 mag for dimmer stars. The shortest cadence for the data is 1 minute (much of the data is spaced 1 minute apart with larger gaps due to nightly/seasonal observations). The data is 99% complete up to a magnitude of GAIA R ~15 mag and begins to saturate at a magnitude of GAIA R ~ 7 mag.
We have shown how the database was created with the intention of making light curves easy to retrieve. During this we also explored how certain features of the data-set, such as the seeing and resolution, were instrumental in the design features of the database, particularly when designing the software to match the same objects across multiple images.
We have also cross-matched the objects in this database with other publicly available databases such as GAIA, 2MASS and WISE in order to gain further information on the population present in this data-set. We may use the additional information provided by GAIA's astrometric data (parallax and proper motion) and stellar colour (provided by GAIA, 2MASS and WISE) to further investigate this stellar population.
We found that the flat frames used for calibration did not produce data of sufficient quality for accurate photometric measurements. A substantial amount of structure is present in some of the flat fields, as it is not possible to know if the structure is truly due to the optical path of the telescope or due to incorrect flat fielding methods. Hence, a photometric correction was performed. The correction procedure removed any systematic photometric offset caused by inhomogeneous flat frames. This was achieved with modelling the photometric offset in a given image that is present in non-variable stars. The model is a function of magnitude, colour and CCD position, and is subtracted from all stars in the image.
We have outlined some of the potential future science projects that can be performed with this data, and show that the database presented in this report is very good for conducting research in the field of time-based astronomy. A preliminary investigation of periodic variable stars was performed. It was found that multiple different types of periodic variables are present in our catalogue such as W Uma binaries and Delta Cepheids. We also investigated the possibility of detecting exoplanet transits and found that it is possible to obtain a photometric accuracy high enough to detect exoplanet transits at the sacrifice of temporal resolution. We found that, if we bin our data to reduce the temporal resolution to 42 minutes, we have a 90\% probability of detecting a hot Jupiter
Molecular jets and outflows from young stellar objects in Cygnus-X, Auriga, and Cassiopeia
Full text linkAn unbiased, systematic survey for jets and outflows from young stars has been performed in two distinct and different regions in the Galactic plane. It utilised the 1 - 0 S(1) near-infrared line of molecular hydrogen (H2) to trace shock-excited emission, using data from the UKIRT Widefield Infrared Survey for H2 (UWISH2) survey. A total of 572 outflows were found in the high-mass star forming complex of Cygnus-X, and 98 in the low-mass regions of Auriga and Cassiopeia. Of these outflows found, 84% are entirely new discoveries, and now 40% of all the currently known H2 outflows are a result of the UWISH2 survey. The properties of the outflows were consistently measured and a large statistical sample has been built. Similarities and differences between the outflow populations in the two regions were explored in order to discover which properties are universal and which depend on local factors. In both regions, most outflows are located in isolated
(60%) and not clustered environments, but those from clusters are longer and more luminous. Almost fifty new infrared cluster candidates have also been discovered as a result of this work, and the typical cluster is around 0.5 pc in diameter. About 10% of outflows form crossing pairs of outflows, and 40% of these show signs of precession compared to 20% in the general population. The outflow position angles are in agreement with a homogeneous distribution. Most of the
outflows are driven by protostars (Class 0/I) rather than the more evolved young stellar objects (Class II), as determined using their mid-infrared magnitudes. The typical outflow has a length of < 0.4 pc, and is slightly asymmetric with one lobe around 30% longer than the other. The length distribution follows an exponential behaviour and there appears to be a maximum length. The typical outflow luminosity is faint (1×10 Lsolar) and most of the outflows are driven by low
or intermediate-luminosity protostars. The lobe luminosity ratios (the faint lobe over the bright lobe) are highly asymmetric in H2. There is a correlation between the length and luminosity of an outflow, and these do not depend on the evolutionary stage of the driving source. There is also a correlation between the luminosity of the driving source and the outflow luminosity, but the length
distribution does not follow their behaviour. Therefore, the outflow lengths must also, to some extent, be governed by the density distribution of the local environment
Statistical inference on the periodicity of irregularly sampled light curves
Full text linkThis thesis deals with the problem of period estimation of irregularly sampled time series, and specifically light curves of variable young stars. Knowing the period of these objects can provide important information about the stars' formation and other characteristics. The light curves are measurements of brightness over time conducted in multiple astronomical filters. We examine this problem from three different points of view. First, we need to obtain an accurate period estimate. For that purpose we introduce a weighted t-process regression model for period estimation as a flexible alternative to Gaussian process regression, since it is common for such data to exhibit a fat-tail behaviour, and we extend these models in order to include measurements from multiple astronomical filters. Secondly, we need to accompany our estimates with some credibility as to whether they represent a real periodic signal. This is usually addressed through hypothesis testing. To that end, we introduce a flexible testing scheme using saddlepoint approximation, that can be applied on a range of periodic models including Gaussian process regression. These tests are also extended for data contaminated with red noise, a type of correlated noise that usually appears in such data. Finally, we explore the asymptotic properties of simple harmonic models with additional red noise and show that this estimates are consistent and asymptotically normal. We test our results through extensive simulation studies which are reported along with an application on some real light curves from the Hunting Outbursting Young Stars citizen science project
Characterising the properties and evolution of surface spots on young stellar objects with citizen science photometry
Full text linkYoung stellar objects (YSOs) display variability on the timescale of the rotational period due to surface spots rotating in and out of the observer’s line of sight. The fast rotation of young stars results in photometric variability on the order of days. In this thesis, a methodology has been developed that uses the peak-to-peak amplitude of variation in multi filter broad band photometry to characterise surface spots on YSOs. This methodology was then applied to data obtained through the Hunting Outbursting Young Stars citizen science project. Firstly, to YSOs in IC 5070 with high cadence data, and then to long duration light curves in the same field. Finally, all YSOs in HOYS fields were searched for periodicity and spot proper ties were established for all suitable sections of light curves. Across all YSO samples, two thirds of spot-induced variability is due to cold spots, and one third is due to warm/hot spots. The majority of all spots detected have surface coverage values below 30 percent. Most cold spots are 300 – 1500 K below the stellar temperature. The threshold of detection is around 300 K above or below the stellar temperature, dependent on coverage. A significant distribution of large, low temperature contrast warm spots (300 – 2500 K above stellar temperature) has been observed, alongside a small population of high temperature (>2500 K above stellar temperature), low coverage hot spots attributed to accretion. Spot properties have been related to stellar properties, particularly inner disc excess. Cold spots appear on objects with no preference to inner disc excess, while warm/hot spots have been observed as more or equally common on objects without an inner disc excess depending on the sample. The observed warm spots are hence either related to accretion as low-density accretion structures, or plages as have been observed on non-accreting YSOs
The structure of molecular clouds
Full text linkThe physics and turbulent properties responsible for shaping the structure in molecular clouds are analysed. Data from the Two-Micron All-Sky Survey are used to determine all-sky median near-infrared extinction maps. Two types of map are made: maps with a near-constant noise in each pixel and maps with a constant resolution. The standard map has a resolution as high as l' along the Galactic plane. The resolution and depth of optical extinction are significantly better than those achieved in previous large-scale studies. The maps are used to examine the column density and mass distributions of 30 nearby molecular clouds. The low column density (i.e. turbulence dominated) parts of the clouds could be well fit by a log-normal distribution. A universal extinction threshold of AV = 5.6 ± 1.2 mag is found, above which there is an excess of material when compared to a log-normal distribution. Gravity is implied as the dominant factor in structure shaping above this threshold, as the column density and mass distributions are similar for all clouds. Below this threshold, the structure is determined by turbulence and the environment of the cloud. Two groups of clouds with distinct column density/mass distributions are identified, that correspond to ‘star forming’ and ‘non-star forming’ groups. Structure function and Δ-variance analyses are performed on the same nearby molecular clouds. Average values are calculated for the structure function parameters A, intermittency, codimension and fractal dimension. The results imply a mixture of solenoidal and compressive forcing in the turbulence dominated regions of the clouds. An average value for the mass index scaling exponent is calculated which is close to the value expected for clouds where turbulence is driven/governed by solenoidal forcing. For the ‘star forming’ clouds the average value implies a mixture of solenoidal and compressive forcing, while the value for the ‘non-star forming’ group implies exclusively solenoidal forcing. It is concluded from this that compressive forcing is associated with the presence of clustered star formation
Statistical Shape Analysis of Galactic Hii Regions
Full text linkHii regions are diffuse nebulae of ionised hydrogen, excited by the extreme ultraviolet emission from massive stars. Due to the embedded nature of massive star formation, there are many observational difficulties involved when investigating such stars. Hii regions, however, are readily observed via their infrared and radio emission. As such, they highlight the location of their massive star sources. Furthermore, Hii region properties are directly resultant of their progenitors and environment. The overall aim of the work presented herein, is to determine whether statistical shape analysis of observational and numerically modelled Hii region data can be used to probe the associated astrophysical properties.
Radio continuum and computer simulated synthetic images of Hii regions were analysed using the shape extraction and statistical comparison methods constructed in this work. For the radio data, six morphological groups were identified. Visual inspection and quantitative ordinance techniques confirmed that the shape analysis and grouping procedure were working as intended. It was found that in the first Galactic quadrant, location is mostly independent of group, with a small preference for regions of similar Galactic longitudes to share common morphologies. The shapes are homogeneously distributed across Galactocentric distance and latitude. One group contained regions that are all younger than 0.5 Myr and ionised by relatively low- to intermediate-mass sources. Those in another group are all driven by intermediate- to high-mass sources. One group was distinctly separated from the other five and contained regions at the surface brightness detection limit for the survey. The hierarchical procedure employed was most sensitive to the spatial sampling resolution used, which is determined for each region from its heliocentric distance.
The numerical Hii region data was the result of photoionisation and feedback of a 34 M⊙ star, in a 1000 M⊙ cloud. Synthetic observations (SOs) were provided, comprising four evolutionary snapshots (0.1, 0.2, 0.4 and 0.6Myr), and multiple viewing projection angles. The shape analysis results provided conclusive evidence of the efficacy of the numerical simulations. When comparing the shapes of the synthetic regions to their observational counterparts, the SOs were grouped in amongst the Galactic Hii regions by the hierarchical procedure. There was also an association between the evolutionary distribution of regions of the respective samples. This suggested that this method could be further developed for classification of the observational regions by using the synthetic data, with its well defined parameters
Properties of Star Clusters
Full text linkStar clusters are tracers of both stellar and Galactic evolution. As such it is essential to analyse their properties and distribution in the Galaxy. Ideally clusters’ fundamental properties (distance, reddening, age, metallicity) should be derived homogeneously, so that their uncertainties are systematic and any global trends identified can be trusted. With the increase
of newly discovered, purely photometric, large cluster samples from infrared surveys such
as 2MASS, WISE, UKIDSS-GPS and VISTA-VVV, new methods to reliably derive these
properties are required.
This Thesis presents novel methods to homogeneously derive the distances, extinctions, ages
and scale height measurements of cluster samples. Distances and extinctions are derived from
photometry alone, without the use of isochrone fitting, and cluster distances can be estimated
with a better than 40% accuracy. Cluster ages are derived using a pipeline which is designed
to consistently determine the values of clusters’ fundamental properties. Novel scale height
measurements are established with a 25% uncertainty for a sample size of 38. Using these methods, the FSR List cluster catalogue is found to be biased towards a distance of 3 kpc and modal age of 400 Myr. A dependence between the interstellar absorption value and Galactic longitude is found, characterised by AH (l)[mag/kpc] = 0.10+0.001 × |l?180 ? |/ ? for regions more than 60 ? from the Galactic Centre.
The temporal scale height evolution of clusters is accurately traced for the first time. A linear
relationship between cluster scale height and log(age/yr) is found which is significantly different from the stellar component of the Galactic Disk. There is also a weak age-independent trend between cluster scale height and Galactocentric distance. No significant temporal or spatial variations of the cluster distribution vertical zero point are found. The Sun’s vertical displacement from the Galactic Plane is measured to be Z? = 18.5 ± 1.2 pc
An analysis on the photometric variability of V 1490 Cyg
Full text linkVariability in Young Stellar Objects (YSOs) is one of their primary characteristics. Long-term, multi-filter, high-cadence monitoring of large samples aids understanding of such sources. Although data from the HOYS citizen science project allows for such monitoring, usage of different filters introduces colour-terms to the photometric data. This thesis outlines the development of a novel colour-term correction method, improving photometric error to within a couple of percent. The corrected light curve for the YSO, V 1490 Cyg, is then discussed in detail.
The source is observed to be a quasi periodic dipper with a period of 31.447 ± 0.011 days. Long and short-term variability is observed for B, V, Rc and Ic data, with larger variability on short timescales for U and Hα. U amplitudes were observed to vary on timescales of hours, indicating the source is still accreting. No significant trends were observed in the structure function, with the amount of mass in the occulting structure seen to vary by up to a factor of 10 for both mass increase and decrease. The lower estimate of the typical accretion rate of V 1490 Cyg was found of the order 10^(−10) Mʘ/year, consistent with low levels of accretion as seen in other T-Tauri stars. Investigating the orbiting structure in V vs. V − Ic parameter space suggests low column density material with roughly ISM dust properties. Embedded in this envelope are denser, small-scale structures, most likely composed of larger dust grains. The scattering properties of this material are consistent and do not change over time. An accurate distance to both IC 5070 and V 1490 Cyg of 870 (+70, −55) pc has been determined using Gaia. Literature near-infrared (NIR) and mid-infrared (MIR) data suggest that V 1490 Cyg is most likely a CTTS, with a currently low, but variable accretion rate. It is potentially at the start of the transition into a WTTS or transition disk object. This thesis finds the nature of the variability of the source is most likely attributed to a protoplanet-induced disk warp
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