Papers by Patricia Whitelock
The Astrophysical Journal, 2017
We have traced the spatial distributions of intermediate-age and old stars in nine dwarf galaxies... more We have traced the spatial distributions of intermediate-age and old stars in nine dwarf galaxies in the distant parts of the Local Group, using multi-epoch 3.6 and 4.5 µm data from the DUST in Nearby Galaxies with Spitzer (DUSTiNGS) survey. Using complementary optical imaging from the Hubble Space Telescope, we identify the tip of the red giant branch (TRGB) in the 3.6 µm photometry, separating thermally-pulsating asymptotic giant branch (TP-AGB) stars from the larger red giant branch (RGB) populations. Unlike the constant TRGB in the I-band, at 3.6 µm the TRGB magnitude varies by ∼0.7 mag, making it unreliable as a distance indicator. The intermediate-age and old stars are well mixed in two-thirds of the sample with no evidence of a gradient in the ratio of the intermediateage to old stellar populations outside the central ∼ 1 − 2. Variable AGB stars are detected in the outer extremities of the galaxies, indicating that chemical enrichment from these dust-producing stars may occur in the outer regions of galaxies with some frequency. Theories of structure formation in dwarf galaxies must account for the lack of radial gradients in intermediate-age populations and the presence of these stars in the outer extremities of dwarfs. Finally, we identify unique features in individual galaxies, such as extended tidal features in Sex A and Sag DIG and a central concentration of AGB stars in the inner regions of NGC 185 and NGC 147.
IAUC 4426 available at Central Bureau for Astronomical Telegrams. IAUC 4426 available at Central ... more IAUC 4426 available at Central Bureau for Astronomical Telegrams. IAUC 4426 available at Central Bureau for Astronomical Telegrams.
ABSTRACT In this study, we investigate the period changes of eight short-period Type II Cepheids ... more ABSTRACT In this study, we investigate the period changes of eight short-period Type II Cepheids of the BL Her subtype, i.e. with periods in the 1–4 d range. The O − C diagrams for these stars are constructed using all suitable observational data from ground and space surveys. This spans a time interval of over one century and includes digitized photographic plates as well as photometry from the literature. The O − C diagrams show parabolic evolutionary trends, which indicate the presence of both increasing and decreasing periods for these eight short-period stars. These period changes are in good agreement with the recent theoretical evolutionary framework and stellar evolution models for BL Her stars. The pulsation stability test proposed by Lombard and Koen also suggests that the changes in the periods are real.
IUE observations providing the first ultraviolet spectroscopic data of the X-ray source Sco X-1 a... more IUE observations providing the first ultraviolet spectroscopic data of the X-ray source Sco X-1 are presented and discussed. The IUE data were obtained in the low resolution mode and cover the wavelength range 1150-3200 A. Data were obtained at many different phases and cycles in the binary period of the system of 0d.8. The short wavelength IUE spectra are dominated
We have carried out an infrared search for obscured asymptotic giant branch (AGB) stars in the Ma... more We have carried out an infrared search for obscured asymptotic giant branch (AGB) stars in the Magellanic Clouds. Fields were observed in the vicinity of lRAS sources with colours and flux densities consistent with such a classification. The survey uncovered a number of obscured AGB stars as well as some supergiants with infrared excess. We present photometry of the sources and discuss the colour diagrams and bolometric luminosities. One of the supergiants is close to the maximum luminosity allowed for red supergiants, implying a progenitor mass around 50 Mo. Its late spectral type (M7.5) is surprising for such a massive star. Most of the AGB stars are luminous, often close to the classical limit of M bol =-7.1. To determine whether the stars are oxygen-rich or carbon-rich, we have acquired narrow-band mid-infrared photometry with the ESO TIMMI camera for several sources. All but one are found to show the silicate feature and therefore to have oxygen-rich dust; the colours of the remaining source are consistent with either an oxygen-rich or a carbon-rich nature. A method to distinguish carbon and oxygen stars based on H-K versus K-[12] colours is presented. We discuss several methods of calculating the mass-loss rate: for the AGB stars the mass-loss rates vary between approximately 5 x 10-4 and 5 x 10-6 Mo yr-\ depending on the assumed dust-togas mass ratio. We present a new way to calculate mass-loss rates from the OR maser emission. We find no evidence for a correlation of the mass-loss rates with luminosity in these obscured stars. Nor do the mass-loss rates for the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) stars differ in any clear systematic way from each other. Expansion velocities appear to be slightly lower in the LMC than in the Galaxy. Period determinations are discussed for two sources: the periods are comparable to those of the longer-period Galactic OR/IR stars. All of the luminous stars for which periods are available have significantly higher luminosities than predicted from the period-luminosity relations.
Proceedings of the International Astronomical Union, Dec 1, 2011
arXiv (Cornell University), Jan 30, 2018
This is a preliminary analysis of the orbital parameters of the well known eclipsing symbiotic bi... more This is a preliminary analysis of the orbital parameters of the well known eclipsing symbiotic binary, SY Muscae. It is a system composed of a white dwarf (WD) and a red giant (RG), located in the southern sky. With the use of photometric data in the infrared (IR) bands and radial velocities (RV) for the RG, we determine physical parameters of the object, such as masses and radii. We use PHOEBE tools to model all the observations.
The astronomer's telegram, Dec 1, 2016
VizieR Online Data Catalog, Nov 1, 2009
American Astronomical Society Meeting Abstracts #231, 2018
We present year-long, near-infrared Hubble Space Telescope WFC3 observations of Mira variables in... more We present year-long, near-infrared Hubble Space Telescope WFC3 observations of Mira variables in the water megamaser host galaxy NGC 4258. Miras are AGB variables that can be divided into oxygen-(O-) and carbon-(C-) rich subclasses. Oxygen-rich Miras follow a tight (scatter ∼ 0.14 mag) Period-Luminosity Relation (PLR) in the near-infrared and can be used to measure extragalactic distances. The water megamaser in NGC 4258 gives a geometric distance to the galaxy accurate to 2.6% that can serve to calibrate the Mira PLR. We develop criteria for detecting and classifying O-rich Miras with optical and NIR data as well as NIR data alone. In total, we discover 438 Mira candidates that we classify with high confidence as O-rich. Our most stringent criteria produce a sample of 139 Mira candidates that we use to measure a PLR. We use the OGLE-III sample of O-rich Miras in the LMC to obtain a relative distance modulus, µ 4258 − µ LM C = 10.95 ± 0.01 (statistical) ±0.06 (systematic) mag which is statistically consistent with the relative distance determined using Cepheids. These results demonstrate the feasibility of discovering and characterizing Miras using the near-infrared with the Hubble Space Telescope and the upcoming James Webb Space Telescope and using them to measure extragalactic distances and determine the Hubble constant.
arXiv (Cornell University), Jul 10, 2020
This White Paper summarizes the discussions from a five-day workshop, involving 50 people from 18... more This White Paper summarizes the discussions from a five-day workshop, involving 50 people from 18 countries, held in Cape Town, South Africa in February 2020. Convened by the International Astronomical Union's Executive Committee Working Group on Global Coordination of Ground and Space Astrophysics and sponsored by the Kavli Foundation, we discussed existing and potential bottlenecks for transient and multi-messenger astronomy, identifying eight broad areas of concern. Some of these are very similar to the challenges faced by many astronomers engaging in international collaboration, for example, data access policies, funding, theoretical and computational resources and workforce equity. Others, including, alerts, telescope coordination and target-of-opportunity implementation, are strongly linked to the time domain and are particularly challenging as we respond to transients. To address these bottlenecks we offer thirty-five specific recommendations, some of which are simply starting points and require development. These recommendations are not only aimed at collaborative groups and individuals, but also at the various organizations who are essential to making transient collaborations efficient and effective: including the International Astronomical Union, observatories, projects, scientific journals and funding agencies. We hope those involved in transient research will find them constructive and use them to develop collaborations with greater impact and more inclusive teams.
arXiv (Cornell University), Jun 22, 2009
Light curves of symbiotic stars in massive photomeric surveys II: S and D'-type systems M. G r o ... more Light curves of symbiotic stars in massive photomeric surveys II: S and D'-type systems M. G r o m a d z k i 1 , J. M i k o ł a j e w s k a 2 , I. S o s z yń s k i 3
Monthly Notices of the Royal Astronomical Society, Dec 1, 1990
La photometrie JHK d'une aire de 1°× 2°, incluant le centre galactique, est presentee. Les di... more La photometrie JHK d'une aire de 1°× 2°, incluant le centre galactique, est presentee. Les diagrammes magnitude-couleur sont analyses. Une carte de l'absorption interstellaire est realisee. La distribution des etoiles, en fonction de la distance angulaire au centre galactique et de la magnitude apparente, est determinee.
HAL (Le Centre pour la Communication Scientifique Directe), 2003
This article presents the study of the light-curves extracted from the MACHO database of a sample... more This article presents the study of the light-curves extracted from the MACHO database of a sample of stars observed by the Infrared Space Observatory in the Small Magellanic Cloud. These stars belong to the ISO-Mini-Survey catalogue of the Magellanic Clouds (ISO-MCMS, Loup et al. in preparation). Most of them are in the asymptotic giant branch (AGB) and supergiant phases. The dominant period and amplitude of pulsation have been derived and the stars have been classified as Mira or Semi-Regular pulsators. Furthermore, the crossidentification with near-infrared DENIS and 2MASS magnitudes available within the ISO-MCMS allowed us: (i) to investigate the properties of these stars in the combined near-and mid-infrared colour-magnitude diagrams, (ii) to derive the bolometric magnitude by integrating the spectral energy distribution and (iii) to estimate the mass-loss rate. The stars have been divided into carbon-(C-) and oxygen-rich (O-rich) using the (J − KS, KS) colour-magnitude diagram and their period and amplitude distributions have been compared. C-rich AGB stars have a sharp peak in their period distribution at about 250 days and have on average a larger amplitude than O-rich AGB stars. This effect, not previously detected from the study of similar stars in the Large Magellanic Cloud and in the Baade's window, might be closely related to the metallicity of the environment in which the stars have formed.
The Astronomical Journal, May 1, 1993
Ultraviolet, optical, and infrared photometry is reported for the symbiotic star AS 296, spanning... more Ultraviolet, optical, and infrared photometry is reported for the symbiotic star AS 296, spanning the first 1200 days of its outburst which began in June 1988. The effects of the outburst were restricted to the wavelength interval 2200<λ<7500 A. The progress of the event was followed through two maxima and two eclipses of the hot source by the M5 III companion. An orbital period of 650 days was derived from the eclipses. At no stage of the outburst did the luminosity approach the Eddington value, and no material was ejected from the system
VizieR Online Data Catalog, 2016
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Papers by Patricia Whitelock