A Proper Motion Survey for White Dwarfs with the Wide Field Planetary Camera 2

We have performed a search for halo white dwarfs as high proper motion objects in a second epoch WFPC2 image of the Groth-Westphal strip. We identify 24 high proper motion objects with mu > 0.014 ''/yr. Five of these high proper motion objects are identified as strong white dwarf candidates on the basis of their position in a reduced proper motion diagram. We create a model of the Milky Way thin disk, thick disk and stellar halo and find that this sample of white dwarfs is clearly an excess above the < 2 detections expected from these known stellar populations. The origin of the excess signal is less clear. Possibly, the excess cannot be explained without invoking a fourth galactic component: a white dwarf dark halo. We present a statistical separation of our sample into the four components and estimate the corresponding local white dwarf densities using only the directly observable variables, V, V-I, and mu. For all Galactic models explored, our sample separates into about 3 disk white dwarfs and 2 halo white dwarfs. However, the further subdivision into the thin and thick disk and the stellar and dark halo, and the subsequent calculation of the local densities are sensitive to the input parameters of our model for each Galactic component. Using the lowest mean mass model for the dark halo we find a 7% white dwarf halo and six times the canonical value for the thin disk white dwarf density (at marginal statistical significance), but possible systematic errors due to uncertainty in the model parameters likely dominate these statistical error bars. The white dwarf halo can be reduced to around 1.5% of the halo dark matter by changing the initial mass function slightly. The local thin disk white dwarf density in our solution can be made consistent with the canonical value by assuming a larger thin disk scaleheight of 500 pc.Comment: revised version, accepted by ApJ, results unchanged, discussion expande

Optimal placement of a limited number of observations for period searches

Robotic telescopes present the opportunity for the sparse temporal placement of observations when period searching. We address the best way to place a limited number of observations to cover the dynamic range of frequencies required by an observer. We show that an observation distribution geometrically spaced in time can minimise aliasing effects arising from sparse sampling, substantially improving signal detection quality. The base of the geometric series is however a critical factor in the overall success of this strategy. Further, we show that for such an optimal distribution observations may be reordered, as long as the distribution of spacings is preserved, with almost no loss of quality. This implies that optimal observing strategies can retain significant flexibility in the face of scheduling constraints, by providing scope for on-the-fly adaptation. Finally, we present optimal geometric samplings for a wide range of common observing scenarios, with an emphasis on practical application by the observer at the telescope. Such a sampling represents the best practical empirical solution to the undersampling problem that we are aware of. The technique has applications to robotic telescope and satellite observing strategies, where target acquisition overheads mean that a greater total target exposure time (and hence signal-to-noise) can often in practice be achieved by limiting the number of observations.Comment: 8 pages with 16 figure

Cosmological Model Predictions for Weak Lensing: Linear and Nonlinear Regimes

Weak lensing by large scale structure induces correlated ellipticities in the images of distant galaxies. The two-point correlation is determined by the matter power spectrum along the line of sight. We use the fully nonlinear evolution of the power spectrum to compute the predicted ellipticity correlation. We present results for different measures of the second moment for angular scales \theta \simeq 1'-3 degrees and for alternative normalizations of the power spectrum, in order to explore the best strategy for constraining the cosmological parameters. Normalizing to observed cluster abundance the rms amplitude of ellipticity within a 15' radius is \simeq 0.01 z_s^{0.6}, almost independent of the cosmological model, with z_s being the median redshift of background galaxies. Nonlinear effects in the evolution of the power spectrum significantly enhance the ellipticity for \theta < 10' -- on 1' the rms ellipticity is \simeq 0.05, which is nearly twice the linear prediction. This enhancement means that the signal to noise for the ellipticity is only weakly increasing with angle for 2'< \theta < 2 degrees, unlike the expectation from linear theory that it is strongly peaked on degree scales. The scaling with cosmological parameters also changes due to nonlinear effects. By measuring the correlations on small (nonlinear) and large (linear) angular scales, different cosmological parameters can be independently constrained to obtain a model independent estimate of both power spectrum amplitude and matter density \Omega_m. Nonlinear effects also modify the probability distribution of the ellipticity. Using second order perturbation theory we find that over most of the range of interest there are significant deviations from a normal distribution.Comment: 38 pages, 11 figures included. Extended discussion of observational prospects, matches accepted version to appear in Ap

Outcome of patients with advanced ovarian cancer who do not undergo debulking surgery: A single institution retrospective review

OBJECTIVE: To assess the outcome of patients with advanced ovarian cancer (OC) who were treated without surgery, having received upfront chemotherapy and no interval debulking surgery (IDS). METHODS: Retrospective analysis of medical and chemotherapy records of consecutive patients with OC between 2005 and 2013 at UCL Hospitals London, UK who received neoadjuvant chemotherapy (NACT) was then found to be unsuitable for IDS following review by the multidisciplinary team. RESULTS: Eighty-three patients (18%) out of 467 receiving NACT did not undergo IDS. Median age was 70years (range 33-88); out of these 83 patients, 43 (51.8%) presented with stage IV disease. Forty-three of these 83 patients received carboplatin and paclitaxel (CP) (51.8%) and 37 received carboplatin alone (C) (44.6%); 3 patients (3.6%) received other platinum-based combinations. Reasons for not proceeding to surgery were: poor response to chemotherapy after 3-4 cycles of NACT (61/83, 73.5%); comorbidities (12/83, 14.5%); patient decision (4/83, 4.8%). Six patients (7.2%) received 2 lines of chemotherapy. In a univariate analysis CP, age <70years, and absence of comorbidities were factors influencing OS. In a multivariate analysis only having received CP remained independently associated with OS (HR 0.49, 95% CI 0.29-0.84). CONCLUSIONS: Chemotherapy alone can provide reasonable disease control in patients unsuitable for IDS and CP should be used if possible

Dust in the Photospheric Environment: Unified Cloudy Models of M, L, and T Dwarfs

We address the problem of how dust forms and how it could be sustained in the static photospheres of cool dwarfs for a long time. In the cool and dense gas, dust forms easily at the condensation temperature, T_cond, and the dust can be in detailed balance with the ambient gas so long as it remains smaller than the critical radius, r_cr. However, dust will grow larger and segregate from the gas when it will be larger than r_cr somewhere at the lower temperature, which we refer to as the critical temperature, T_cr. Then, the large dust grains will precipitate below the photosphere and only the small dust grains in the region of T_cr < T < T_cond can be sustained in the photosphere. Thus a dust cloud is formed. Incorporating the dust cloud, non-grey model photo- spheres in radiative-convective equilibrium are extended to T_eff as low as 800K. Observed colors and spectra of cool dwarfs can consistently be accounted for by a single grid of our cloudy models. This fact in turn can be regarded as supporting evidence for our basic assumption on the cloud formation.Comment: 50 pages with 14 postscript figures, to be published in Astrophys.

Switching from standard to dose-dense chemotherapy in front-line treatment of advanced ovarian cancer: a retrospective study of feasibility and efficacy

BACKGROUND: Current standard neoadjuvant treatment for advanced ovarian cancer is 3-weekly platinum-based chemotherapy (CP3w). Patients unable to have interval debulking surgery (IDS) or with significant residual disease have a poor outcome to CP3w treatment. We investigated the outcome in patients who were switched to dose-dense chemotherapy. METHODS: We retrospectively analysed 30 patients treated at UCLH in 2009–2013, who switched to dose-dense chemotherapy after neoadjuvant CP3w, having achieved a poor response/progressed and unable to proceed to IDS (n=21), or had >1 cm residual disease after IDS (n=9). Treatment was 3-weekly carboplatin and weekly paclitaxel (n=23), or both drugs weekly (n=7). For comparison, we included 30 matched patients treated with CP3w followed by IDS (n=24, without or ≤1 cm residual disease; n=6, with >1 cm residual disease). Time to progression (TTP) and overall survival (OS) were measured from the date of diagnosis until progression (CT scan or CA-125) and death from any cause, respectively. RESULTS: Baseline characteristics were similar in both groups. The response rate to dose-dense chemotherapy was 70% (Gynecological Cancer Intergroup criteria). In the dose-dense group, 24 patients had tumour progression and 16 died; the corresponding numbers in the control group were 24 and 11. Median TTP was 15.8 months with dose-dense therapy, higher than expected for this patient group, and the same as in the control group (15.7 months) undergoing IDS, p=0.27. Median TTP in patients with residual disease postsurgery was 16.5 months (dose-dense) and 10.8 months (controls), p=0.02. TTP in dose-dense patients who did not have surgery was 10.4 months. Median OS was 31.3 (dose-dense) and 59.6 months (controls), p=0.06. Dose-dense chemotherapy was well tolerated: only three patients interrupted treatment due to toxicity. CONCLUSION: Switching to dose-dense chemotherapy in patients who failed to respond to CT3w neoadjuvant chemotherapy appears to be an effective strategy and requires further investigation

Hubble Space Telescope Imaging of the Circumstellar Nebulosity of T Tauri

Short-exposure Planetary Camera images of T Tauri have been obtained using broadband filters spanning the wavelength range 0.55-0.80 μm. The optically visible star lies very close to an arc of reflection nebulosity. The arc's northern arm extends approximately 5" from the star, while its southwestern arm appears brighter and extends only 2". The arc shows an approximate symmetry along an axis toward the west-northwest, the direction of Hind's Nebula and the blueshifted molecular outflow. The morphology of the reflected light is similar to models of scattered light within an illuminated, axisymmetric outflow cavity in a circumbinary envelope, viewed ≈ 45° from the outflow axis. However, our model images do not successfully account for the amount of limb brightening that is seen. No optical counterpart to the infrared companion is seen to a limiting magnitude of V = 19.6, which suggests A_V > 7 mag toward this source. There is no evidence for an optical tertiary, to a limiting ΔV = 5.1 mag fainter than the primary, at the position where such an object has been previously reported

Mainstreamed Genetic Testing in Ovarian Cancer: Patient Experience of the Testing Process

Objective: Pathogenic BRCA variants account for between 5.8-24.8% of ovarian cancers. The identification of such a variant can have a significant impact on the affected individual and their relatives – determining eligibility for targeted therapies, predicting treatment response and granting access to disease prevention strategies. Cancer services are responding to the increased demand for genetic testing with the introduction of mainstreamed genetic testing via oncology clinics. The study aimed to evaluate patient experience of the mainstreamed genetic testing pathway at a tertiary referral centre in London. / Methods: Study participants were patients diagnosed with high-grade non-mucinous ovarian cancer, tested via a mainstreamed genetic testing pathway at the tertiary referral centre between February 2015 and June 2017. Eligible participants were invited to complete the retrospective study questionnaire. Five quantitative measures with additional free-text items evaluated the patient experience of mainstreamed genetic testing. / Results: The tertiary referral centre tested 170 ovarian cancer patients. Twenty-three pathogenic BRCA mutations were identified (23/170, 13.5%). One-hundred and six patients (106/170, 62.4%) met the study inclusion criteria. Twenty-nine of those invited (29/106, 27.4%) to participate returned the retrospective study questionnaire. Pathogenic BRCA1/2 variants were identified within four respondents (4/29, 13.8%). Motivations for genetic testing related to improved medical management, and the ability to provide relatives with genetic information. Participants did not appear to be adversely affected by result disclosure post mainstreamed genetic testing. Two individuals with a pathogenic variant reported that the support provided by the tertiary referral centre post-result disclosure could have been improved. / Conclusion: Results of the current study support further psychosocial research into the expansion of the mainstreamed genetic testing pathway. The results although promising have also highlighted the importance of genetic awareness within the multidisciplinary team and the provision of timely psychological support from genetic specialists