Papers by Despina Hatzidimitriou
New Results of Nearby Aged Planetary Nebulae
VizieR Online Data Catalog: Pismis 18 photometry and radial velocities (Hatzidimitriou+, 2019)
VizieR Online Data Catalog, Jun 1, 2019
CCD observations of binary clusters in the Magellanic Clouds
European Southern Observatory Conference and Workshop Proceedings, 1987
VizieR Online Data Catalog: VI magnitudes of NGC 4535 stars (Spetsieri+, 2018)
VizieR Online Data Catalog, Aug 1, 2018
Small Magellanic Cloud: Star-Formation History and X-Ray Binary Populations
ASPC, Jul 1, 2010
Using Chandra, XMM-Newton and optical photometric catalogs we study the young XRB populations of ... more Using Chandra, XMM-Newton and optical photometric catalogs we study the young XRB populations of the SMC. We find that the Be-XRBs are observed in regions with star formation (SF) rate bursts ∼25-60 Myr ago. The similarity of this age with the age of maximum occurrence of the Be phenomenon (∼40 Myr) indicates that the presence of a circumstellar decretion disk plays a significant role in the number of observed XRBs in the 10-100 Myr age range. We also find that regions with strong but more recent SF (e.g. the Wing) are deficient in Be-XRBs. By correlating the number of observed Be-XRBs with the formation rate of their parent populations, we measure a Be-XRB production rate of ∼1 system per 10^{−3} M⊙/yr. Finally, we use the strong localization of the Be-XRB systems in order to set limits on the kicks imparted on the neutron star during the supernova explosion.
arXiv (Cornell University), Nov 30, 2017
We aim to construct an exceptionally deep (V 27) catalog of variable objects in selected Galactic... more We aim to construct an exceptionally deep (V 27) catalog of variable objects in selected Galactic and extragalactic fields visited multiple times by the Hubble Space Telescope (HST). While HST observations of some of these fields were searched for specific types of variables before (most notably, the extragalactic Cepheids), we attempt a systematic study of the population of variable objects of all types at the magnitude range not easily accessible with ground-based telescopes. The variability timescales that can be probed range from hours to years depending on how often a particular field has been visited. For source extraction and cross-matching of sources between visits we rely on the Hubble Source Catalog which includes 10 7 objects detected with WFPC2, ACS, and WFC3 HST instruments. The lightcurves extracted from the HSC are corrected for systematic effects by applying local zero-point corrections and are screened for bad measurements. For each lightcurve we compute variability indices sensitive to a broad range of variability types. The indices characterize the overall lightcurve scatter and smoothness. Candidate variables are selected as having variability index values significantly higher than expected for objects of similar brightness in the given set of observations. The Hubble Catalog of Variables will be released in 2018.
VizieR Online Data Catalog: SMC RR Lyrae Fourier decomposition (Kapakos+, 2012)
Publications of the Astronomical Society of Australia, 1992
The 1980s saw a surge of research into dwarf galaxies due to the advent of high quantum efficienc... more The 1980s saw a surge of research into dwarf galaxies due to the advent of high quantum efficiency optical detectors and low system noise radio receivers. Astronomers from Australia have been very active in this field, and will continue to be so as new avenues of research into dwarf galaxies continue to open up in the 1990s with the introduction of infrared arrays, high-throughput spectrographs, new mm wavelength and radio telescopes/interferometers, larger optical telescopes, and even more powerful computers. Cognisant of these developments and the fact that the last major symposium devoted to dwarf galaxies was held six years ago (viz., Star-forming dwarf galaxies and related objects, held in Paris, 1985), staff at the Anglo-Australian Observatory decided to hold a one-day conference on Australian research on dwarf galaxies. The meeting was held on 29 April 1991 at the CSIRO Division of Radiophysics and ATNF in Epping NSW. It was a well attended conference with 14 speakers and 38 participants. This set of abstracts covers 12 of the talks from the conference. More information can be obtained from the individual authors at their institutions. Classification and Evolution of Dwarf Galaxies Gerhardt R. Meurer (Anglo-Australian Observatory) The properties of dwarf galaxies are reviewed with the emphasis placed on biases produced by selection effects. The selection effects involved are the inclusion criteria in galaxy catalogues, and the criteria for dwarf/normal galaxy separation. Common selection criteria are luminosity, surface brightness, compactness, colour, the presence of emission lines, and the ability to discern an object against the background of the night sky. Important results which are not by-products of selection effects include: (1) dwarf galaxies fall into two familiesthe gas rich dwarf irregulars (dl) and blue compact dwarfs (BCD) and the gas poor dwarf elliptical (dE), dwarf spheroidal (dSph), and compact elliptical (cE) galaxies; (2) nearly all dwarf galaxies, except for the cEs, can be characterised by an exponential distribution of light; (3) all dwarf galaxies with detectable amounts of HI show signs of recent star formation; (4) dEs often have nuclei, dls never have nuclei, and BCDs sometimes have nuclei. Possible evolutionary links between the different types are discussed in the light of these results.
Workshop on ``Astronomy in High Education in Greece
ABSTRACT
Astronomy from Wide-Field Imaging, 1994
More than 1000 new carbon stars have been identified in a-200 deg 2 area of the SMC during a surv... more More than 1000 new carbon stars have been identified in a-200 deg 2 area of the SMC during a survey of UK Schmidt Telescope objective-prism plates. Their spatial distribution is like that of the red horizontal branch stars.
Probing the Extinction in M31 via a Spectrum of a Quasar Seen through its Disk
AIP Conference Proceedings, 2011
... We check the pencil beam values along the sightline of N21 from the Westerbork HI gas map (Br... more ... We check the pencil beam values along the sightline of N21 from the Westerbork HI gas map (Brinks and Shane [15]) and derive a column density N ... Ivezić, S. Kent, PZ Kunszt, DQ Lamb, RF Leger, DC Long, J. Loveday, RH Lupton, A. Meiksin, A. Merelli, JA Munn, HJ Newberg, M ...
Cluster pairs in the Small Magellanic Cloud
Astronomy & Astrophysics - ASTRON ASTROPHYS, 1990
The cluster system of the SMC has been surveyed with the aim of identifying close pairs of cluste... more The cluster system of the SMC has been surveyed with the aim of identifying close pairs of clusters. It is found that the number of existing close cluster pairs is significantly (at the 3.5 sigma level) larger than the expected number of such pairs due to the chance line-up of single clusters, implying that some of these pairs are physically associated. Comparison with the LMC cluster system shows that the ratio of pairs is similar to the ratio of single clusters in the two galaxies. These results, combined with the earlier results for the LMC, indicate the tendency of clusters to form in pairs, or possibly in groups, at least in the case of irregular galaxies, the probability that the observed number of pairs having formed due to tidal capture being small.
The cluster system of the Large Magellanic Cloud
Astronomy and …, 1990
... I ~L-V6~ L~' I' ~9At1 96 `I 61' ?1' 2. S9 9LI ~t' ~` 9~' D Z&#x... more ... I ~L-V6~ L~' I' ~9At1 96 `I 61' ?1' 2. S9 9LI ~t' ~` 9~' D Z'~C i' ~` 0L oc IILIN S~'t `I 6i~ ~ L~ i'i' L9 Li' ~` c6 `I OCT 9~ ZI OL-£~` I' £ZSH `*I ~*9 LI ... L~r ~ cLCI `I L1'T ~`I ~9-tLZ LCI'SH f'LN oIC O~ Cf~ L9 V?J O~ ~ ~CL~IS ~T s~ 69-16C L~' ~ LI'~SH ~LCT `I 86 9~ cL SLT ~L'IS CLH ~j 6 ...
New Results on the Magellanic Clouds
Astronomy from Wide-Field Imaging, 1994
Recent results on global properties of the Magellanic Clouds are reviewed, with particular emphas... more Recent results on global properties of the Magellanic Clouds are reviewed, with particular emphasis on the impact of wide-field techniques on their study. The subjects discussed include large-scale surveys of different tracers of intermediate age and old populations in the Clouds and new data on their chemical evolution, kinematics and spatial motion.
arXiv: Instrumentation and Methods for Astrophysics, 2019
This is the MSE Detailed Science Case (DSC). It is the highest level document in the MSE document... more This is the MSE Detailed Science Case (DSC). It is the highest level document in the MSE document hierarchy, and forms the foundation for the Level 0 Science Requirements Document (SRD). A snapshot of the entire MSE observatory including technical designs at the end of the Conceptual Design Phase can be found in The MSE Book 2018. The MSE DSC provides the science narrative describing the principal envisioned science goals of MSE and describes its impact on a broad range of science topics. This new version of the DSC builds upon, develops and augments the original science case that was released in 2016. It reaffirms the science capabilities of MSE that form the basis of the SRD, while updating it for recent advances and discoveries (e.g., Data Release 2 of Gaia, GW170817, ...). It includes new contributions and perspectives from the science team, whose membership has grown significantly since 2016 (> 360 members in 2019 compared to ∼ 100 members in 2016; for a full list of current science team members, please refer to the Appendix). A note on the structure of the DSC The structure of Version 2 of the DSC is notably different from the original version. The DSC begins with an Executive Summary and an Overview chapter, after which there are seven thematic chapters that describe the science cases for MSE from exoplanetary through to cosmological scales. Each chapter was developed by the relevant thematic Science Working Group (SWGs). Each chapter can be read as a stand-alone document.
Dynamical and Spectral Properties of Some Double Clusters in the LMC
The World of Galaxies, 1989
Pursuant to Bhatia and Hatzidimitriou's (1988) suggestion as to the existence of binary s... more Pursuant to Bhatia and Hatzidimitriou's (1988) suggestion as to the existence of binary star clusters in the LMC, a dynamical and star-population study was conducted for some of the cataloged candidate pairs. Positive evidence was obtained of significant distortions in cluster density profiles, especially in the outer regions; these disturbances are interpreted as indicators of dynamical interaction between pair members.
Monthly Notices of the Royal Astronomical Society, 2004
From a sample of 304 carbon stars in the central parts of the Large Magellanic Cloud (LMC), ∼27 p... more From a sample of 304 carbon stars in the central parts of the Large Magellanic Cloud (LMC), ∼27 per cent have Merrill-Sanford (MS) bands of the SiC 2 molecule. The data are based on a uniform set of spectra taken with 2dF on the Anglo-Australian Telescope, and give useful statistics on the incidence of MS bands and on their correlation (or otherwise) with other properties. All of these are red stars, cooler than 3100 K. The proportion of stars showing the bands is highest amongst the coolest stars, but not all very cool stars show the bands. There is no evidence that MS bands are more common in J-type stars (carbon stars with a high 13 C/ 12 C ratio) than in N-type carbon stars, at least within this sample of LMC stars. There is no apparent correlation with stellar variability, or between the photospheric temperature [as measured by (J − K)] and the occurrence of the 'hot' MS bands from excited molecular states.
Monthly Notices of the Royal Astronomical Society, 2003
A sample of 1497 carbon stars in the Large Magellanic Cloud (LMC) has been observed in the red pa... more A sample of 1497 carbon stars in the Large Magellanic Cloud (LMC) has been observed in the red part of the spectrum with the 2dF facility on the Anglo-Australian Telescope. Of these, 156 have been identified as J-type (i.e. 13 C-rich) carbon stars using a technique which provides a clear distinction between J stars and the normal N-type carbon stars that comprise the bulk of the sample, and yields few borderline cases. A simple two-dimensional classification of the spectra, based on their spectral slopes in different wavelength regions, has been constructed and found to be related to the more conventional c and j indices, modified to suit the spectral regions observed. Most of the J stars form a photometric sequence in the K − (J − K) colour-magnitude diagram, parallel to and 0.6 mag fainter than the N-star sequence. A subset of the J stars (about 13 per cent) are brighter than this J-star sequence; most of these are spectroscopically different from the other J stars. The bright J stars have stronger CN bands than the other J stars and are found strongly concentrated in the central regions of the LMC. Most of the rather few stars in common with Hartwick and Cowley's sample of suspected CH stars are J stars. Overall, the proportion of carbon stars identified as J stars is somewhat lower than has been found in the Galaxy. The Na D lines are weaker in the LMC J stars than in either the Galactic J stars or the LMC N stars, and do not seem to depend on temperature.
Astronomy & Astrophysics, 2013
Context. Local-Group galaxies provide access to samples of X-ray source populations of whole gala... more Context. Local-Group galaxies provide access to samples of X-ray source populations of whole galaxies. The XMM-Newton survey of the Small Magellanic Cloud (SMC) completely covers the bar and eastern wing with a 5.6 deg 2 area in the (0.2−12.0) keV band. Aims. To characterise the X-ray sources in the SMC field, we created a catalogue of point sources and sources with moderate extent. Sources with high extent (≥40) have been presented in a companion paper. Methods. We searched for point sources in the EPIC images using sliding-box and maximum-likelihood techniques and classified the sources using hardness ratios, X-ray variability, and their multi-wavelength properties. Results. The catalogue comprises 3053 unique X-ray sources with a median position uncertainty of 1.3 down to a flux limit for point sources of ∼10 −14 erg cm −2 s −1 in the (0.2−4.5) keV band, corresponding to 5 × 10 33 erg s −1 for sources in the SMC. We discuss statistical properties, like the spatial distribution, X-ray colour diagrams, luminosity functions, and time variability. We identified 49 SMC high-mass X-ray binaries (HMXB), four super-soft X-ray sources (SSS), 34 foreground stars, and 72 active galactic nuclei (AGN) behind the SMC. In addition, we found candidates for SMC HMXBs (45) and faint SSSs (8) as well as AGN (2092) and galaxy clusters (13). Conclusions. We present the most up-to-date catalogue of the X-ray source population in the SMC field. In particular, the known population of X-ray binaries is greatly increased. We find that the bright-end slope of the luminosity function of Be/X-ray binaries significantly deviates from the expected universal high-mass X-ray binary luminosity function.
Novae as supersoft X-ray sources in the Andromeda galaxy
The X-ray Universe 2014, Jul 1, 2014
Novae are the major class of supersoft X-ray sources (SSSs) in the central region of our neighbou... more Novae are the major class of supersoft X-ray sources (SSSs) in the central region of our neighbouring galaxy Andromeda (M31). From 2006 until 2012 we carried out a dedicated monitoring of the M31 central region with XMM-Newton and Chandra that was specifically designed to detect and characterise SSS states of novae. Only X-ray observations allow us to observe the hot post-nova white dwarf directly and study its physics. Here, I present new results based on an updated catalogue of 79 novae with SSS counterparts, which is by far the largest sample known in any galaxy, to date. Global trends and correlations were established between various multiwavelength nova parameters and there appear to be significant deviations from current models of Galactic novae. Furthermore, there is evidence for different X-ray parameters of sub-samples associated with the M31 bulge and disk, although the question whether both populations are inherently different is far from resolved. The sample contains several remarkable individual novae and I will discuss their peculiarities and importance. The X-ray monitoring of large, homogeneous samples of extragalactic novae is shown to be a powerful tool to study nova populations and the dependence of their observable characteristics on the underlying stellar population
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Papers by Despina Hatzidimitriou