The POINT–AGAPE (Pixel-lensing Observations with the Isaac Newton Telescope–Andromeda Galaxy Amplified Pixels Experiment) survey is an optical search for gravitational microlensing events towards the ...Andromeda galaxy (M31). As well as microlensing, the survey is sensitive to many different classes of variable stars and transients. In our first paper of this series, we reported the detection of 20 classical novae (CNe) observed in Sloan r′ and i′ passbands. An analysis of the maximum magnitude versus rate of decline (MMRD) relationship in M31 is performed using the resulting POINT–AGAPE CN catalogue. Within the limits of the uncertainties of extinction internal to M31, good fits are produced to the MMRD in two filters. The MMRD calibration is the first to be performed for Sloan r′ and i′ filters. However, we are unable to verify that novae have the same absolute magnitude 15 d after peak (the t15 relationship), nor any similar relationship for either Sloan filter. The subsequent analysis of the automated pipeline has provided us with the most thorough knowledge of the completeness of a CN survey to date. In addition, the large field of view of the survey has permitted us to probe the outburst rate well into the galactic disc, unlike previous CCD imaging surveys. Using this analysis, we are able to probe the CN distribution of M31 and evaluate the global nova rate. Using models of the galactic surface brightness of M31, we show that the observed CN distribution consists of a separate bulge and disc population. We also show that the M31 bulge CN eruption rate per unit r′ flux is more than five times greater than that of the disc. Through a combination of the completeness, M31 surface brightness model and our M31 CN eruption model, we deduce a global M31 CN rate of 65+16−15 yr−1, a value much higher than found by previous surveys. Using the global rate, we derive a M31 bulge rate of 38+15−12 yr−1 and a disc rate of 27+19−15 yr−1. Given our understanding of the completeness and an analysis of other sources of error, we conclude that the true global nova rate of M31 is at least 50 per cent higher than was previously thought and this has consequent implications for the presumed CN rate in the Milky Way. We deduce a Galactic bulge rate of 14+6−5 yr−1, a disc rate of 20+14−11 yr−1 and a global Galactic rate of 34+15−12 yr−1, consistent with the Galactic global rate derived elsewhere by independent methods.
The POINT-AGAPE collaboration is carrying out a search for gravitational microlensing toward M31 to reveal galactic dark matter in the form of MACHOs (Massive Astrophysical Compact Halo Objects) in ...the halos of the Milky Way and M31. A high-threshold analysis of 3 years of data yields 6 bright, short-duration microlensing events, which are confronted to a simulation of the observations and the analysis. The observed signal is much larger than expected from self lensing alone and we conclude, at the 95% confidence level, that at least 20% of the halo mass in the direction of M31 must be in the form of MACHOs if their average mass lies in the range 0.5-1 M. This lower bound drops to 8% for MACHOs with masses 60.01 M. In addition, we discuss a likely binary microlensing candidate with caustic crossing. Its location, some 32' away from the centre of M31, supports our conclusion that we are detecting a MACHO signal in the direction of M31.
Searching for microlensing in M31 using automated superpixel surveys raises a number of difficulties which are not present in more conventional techniques. Here we focus on the problem that the list ...of microlensing candidates is sensitive to the selection criteria or ‘cuts’ imposed, and some subjectivity is involved in this. Weakening the cuts will generate a longer list of microlensing candidates but with a greater fraction of spurious ones; strengthening the cuts will produce a shorter list but may exclude some genuine events. We illustrate this by comparing three analyses of the same data set obtained from a 3 yr observing run on the Isaac Newton Telescope in La Palma. The results of two of these analyses have been already reported: Belokurov et al. obtained between three and 22 candidates, depending on the strength of their cuts, while Calchi Novati et al. obtained six candidates. The third analysis is presented here for the first time and reports 10 microlensing candidates, seven of which are new. Only two of the candidates are common to all three analyses. In order to understand why these analyses produce different candidate lists, a comparison is made of the cuts used by the three groups. Particularly crucial are the method employed to distinguish between a microlensing event and a variable star, and the extent to which one encodes theoretical prejudices into the cuts. Another factor is that the superpixel technique requires the masking of resolved stars and bad pixels. Belokurov et al. and the present analysis use the same input catalogue and the same masks but Calchi Novati et al. use different ones and a somewhat less automated procedure. Because of these considerations, one expects the lists of candidates to vary and it is not possible to pronounce a candidate a definite microlensing event. Indeed we accept that several of our new candidates, especially the long time-scale ones, may not be genuine. This uncertainty also impinges on one of the most important goals of these surveys, which is to place constraints on the massive compact halo object (MACHO) fraction in M31. Such constraints depend on using Monte Carlo simulations to carry out an efficiency analysis for microlensing detection, and the results should be relatively insensitive to the selection criteria provided the simulations employ the same cuts as the pipelines. Calchi Novati et al. have already derived the constraints associated with their analysis and we present here the constraints associated with the most recent analysis. The constraints are similar if we neglect our long time-scale events and comparable to those found for MACHOs in our own Galaxy by earlier microlensing surveys of the Magellanic Clouds. However, our constraints are different from those of Calchi Novati et al. if we include our long time-scale events.
For the purposes of identifying microlensing events, the POINT-AGAPE collaboration has been monitoring the Andromeda galaxy (M31) for three seasons (1999-2001) with the Wide Field Camera on the Isaac ...Newton Telescope. In each season, data are taken for one hour per night for roughly 60 nights during the six months that M31 is visible. The two 33 × 33 arcmin2 fields of view straddle the central bulge, northwards and southwards. We have calculated the locations, periods and brightness of 35 414 variable stars in M31 as a by-product of the microlensing search. The variables are classified according to their period and brightness. Rough correspondences with classical types of variable star (such as Population I and II Cepheids, Miras and semiregular long-period variables) are established. The spatial distribution of Population I Cepheids is clearly associated with the spiral arms, while the central concentration of the Miras and long-period variables varies noticeably, the brighter and the shorter period Miras being much more centrally concentrated. A crucial role in the microlensing experiment is played by the asymmetry signal - the excess of events expected in the southern or more distant fields as measured against those in the northern or nearer fields. It was initially assumed that the variable star populations in M31 would be symmetric with respect to the major axis, and thus variable stars would not be a serious contaminant for measuring the microlensing asymmetry signal. We demonstrate that this assumption is not correct. All the variable star distributions are asymmetric primarily because of the effects of differential extinction associated with the dust lanes. The size and direction of the asymmetry of the variable stars is measured as a function of period and brightness. The implications of this discovery for the successful completion of the microlensing experiments towards M31 are discussed.
We have carried out a survey of the Andromeda galaxy for unresolved microlensing (pixel lensing). We present a subset of four short timescale, high signal-to-noise microlensing candidates found by ...imposing severe selection criteria: the source flux variation exceeds the flux of an $R=21$ magnitude star and the full width at half maximum timescale is less than 25 days. Remarkably, in three out of four cases, we have been able to measure or strongly constrain the Einstein crossing time of the event. One event, which lies projected on the M 31 bulge, is almost certainly due to a stellar lens in the bulge of M 31. The other three candidates can be explained either by stars in M 31 and M 32 or by MACHOs.
ABSTRACT
The POINT–AGAPE (Pixel‐lensing Observations with the Isaac Newton Telescope–Andromeda Galaxy Amplified Pixels Experiment) survey is an optical search for gravitational microlensing events ...towards the Andromeda galaxy (M31). As well as microlensing, the survey is sensitive to many different classes of variable stars and transients. Here we describe the automated detection and selection pipeline used to identify M31 classical novae (CNe) and we present the resulting catalogue of 20 CN candidates observed over three seasons. CNe are observed both in the bulge region as well as over a wide area of the M31 disc. Nine of the CNe are caught during the final rise phase and all are well sampled in at least two colours. The excellent light‐curve coverage has allowed us to detect and classify CNe over a wide range of speed class, from very fast to very slow. Among the light curves is a moderately fast CN exhibiting entry into a deep transition minimum, followed by its final decline. We have also observed in detail a very slow CN which faded by only 0.01 mag d−1 over a 150‐d period. We detect other interesting variable objects, including one of the longest period and most luminous Mira variables. The CN catalogue constitutes a uniquely well‐sampled and objectively‐selected data set with which to study the statistical properties of CNe in M31, such as the global nova rate, the reliability of novae as standard‐candle distance indicators and the dependence of the nova population on stellar environment. The findings of this statistical study will be reported in a follow‐up paper.
An automated search is carried out for microlensing events using a catalogue of 44 554 variable superpixel light curves derived from our 3-yr monitoring programme of M31. Each step of our candidate ...selection is objective and reproducible by a computer. Our search is unrestricted, in the sense that it has no explicit time-scale cut. So, it must overcome the awkward problem of distinguishing long time-scale microlensing events from long-period stellar variables. The basis of the selection algorithm is the fitting of the superpixel light curves to two different theoretical models, using variable star and blended microlensing templates. Only if microlensing is preferred is an event retained as a possible candidate. Further cuts are made with regard to: (i) sampling, (ii) goodness of fit of the peak to a Paczyński curve, (iii) consistency of the microlensing hypothesis with the absence of a resolved source, (iv) achromaticity, (v) position in the colour-magnitude diagram and (vi) signal-to-noise ratio. Our results are reported in terms of first-level candidates, which are the most trustworthy, and second-level candidates, which are possible microlensing events but have a lower signal-to-noise ratio and are more questionable. The pipeline leaves just three first-level candidates, all of which have very short full-width at half-maximum time-scales (t1/2 < 5 d) and three second-level candidates, which have time-scales of t1/2 = 31, 36 and 51 d. We also show 16 third-level light curves, as an illustration of the events that just fail the threshold for designation as microlensing candidates. They are almost certainly mainly variable stars. Two of the three first-level candidates correspond to known events (PA 00-S3 and 00-S4) already reported by the POINT-AGAPE project. The remaining first-level candidate is new. This algorithm does not find short time-scale events that are contaminated with flux from nearby variable stars (such as PA 99-N1).
The light curve of PA-99-N2, one of the recently announced microlensing candidates toward M31, shows small deviations from the standard Paczynski form. We explore a number of possible explanations, ...including correlations with the seeing, the parallax effect, and a binary lens. We find that the observations are consistent with an unresolved red giant branch or asymptotic giant branch star in M31 being microlensed by a binary lens. We find that the best-fit binary lens mass ratio is approx1.2 x 10 super(-2), which is one of the most extreme values found for a binary lens so far. If both the source and lens lie in the M31 disk, then the standard M31 model predicts the probable mass range of the system to be 0.02-3.6 M sub(o) (95% confidence limit). In this scenario, the mass of the secondary component is therefore likely to be below the hydrogen-burning limit. On the other hand, if a compact halo object in M31 is lensing a disk or spheroid source, then the total lens mass is likely to lie between 0.09 and 32 M sub(o), which is consistent with the primary being a stellar remnant and the secondary being a low-mass star or brown dwarf. The optical depth (or, alternatively, the differential rate) along the line of sight toward the event indicates that a halo lens is more likely than a stellar lens, provided that dark compact objects comprise no less than 15% (or 5%) of halos.
Ce texte étudie la construction des liens de filiation et les divers achoppements de leur réalisation. Il se centre d’abord sur l’adoption du jeune enfant (moins de trois ans). Les parents vont aider ...l’enfant à se situer dans une histoire commune, à partir de l’intégration du passé tant le leur propre que celui de leur enfant. Cette co-création peut advenir sans que le passé de l’enfant soit occulté ou qu’une trop grande importance soit donnée à ces premiers temps. Il y a création d’une fiction fondatrice, fiction de scène primitive, comme si les parents étaient vraiment à l’origine de cet enfant et comme si l’enfant pensait qu’il aurait pu être issu de leur union. Un exemple clinique d’une patiente suivie en psychothérapie indique qu’enfant elle ne s’est pas laissée adopter même si elle a bénéficié de parents adoptifs apparemment de bonne qualité. D’autres vignettes cliniques montrent qu’avant même l’arrivée de l’enfant dans leur foyer, des parents peuvent révéler des difficultés, des taches aveugles qui demandent à être mises au travail pour permettre au processus d’adoption ou d’adoptabilité de se mettre en place, avant même la rencontre parents–enfant. Enfin, sont abordées les difficultés particulières de l’adoption tardive. Des exemples cliniques exposent là encore que tous les enfants ne sont pas adoptables et que tous les parents n’ont pas les capacités adoptives nécessaires pour ce type d’adoption requérant des mécanismes de défense souples qui permettent de faire face aux conflits qui ne manqueront pas d’apparaître. L’accompagnement psychologique de l’adoption vise à permettre et soutenir un travail de pensée autour de la filiation chez les parents et leurs enfants.
This paper investigates the construction of kinship ties and the various stumbling blocks to their achievement. It first focuses on the adoption of young children (under three years). Parents help the child to find its place in a common history, through the integration of their own past as well as the child's. This co-creation can happen without concealing the past of the child or giving too much emphasis to those early days. There is a creation of a founding fiction, primal scene fiction, as if the parents were really behind this child and as if the child thought he could have been born of their union. A clinical example of a patient followed in psychotherapy shows that when she was a child she did not let herself be adopted even though she had received adoptive parents who seemed to be perfectly acceptable. Other clinical vignettes show that even before the arrival of the child in their home, parents may reveal difficulties, blind spots that need to be worked on in order to implement the adoption or adoptability, even before the parent-child process. Finally, the particular difficulties of not all late adoption are discussed. Clinical examples show again that not all children are adoptable and that not all parents have the capacity to foster this type of adoption requiring strength, flexibility and distancing to manage conflicts that are bound to appear. Work within a structure underpinned by adoption counseling, aims to enable and support thought about parentage among parents and their children.
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