5 research outputs found
Age determination of the HR8799 planetary system using asteroseismology
Discovery of the first planetary system by direct imaging around HR8799 has
made the age determination of the host star a very important task. This
determination is the key to derive accurate masses of the planets and to study
the dynamical stability of the system. The age of this star has been estimated
using different procedures. In this work we show that some of these procedures
have problems and large uncertainties, and the real age of this star is still
unknown, needing more observational constraints. Therefore, we have developed a
comprehensive modeling of HR8799, and taking advantage of its gamma
Doradus-type pulsations, we have estimated the age of the star using
asteroseismology. The accuracy in the age determination depends on the rotation
velocity of the star, and therefore an accurate value of the inclination angle
is required to solve the problem. Nevertheless, we find that the age estimate
for this star previously published in the literature ([30,160] Myr) is
unlikely, and a more accurate value might be closer to the Gyr. This
determination has deep implications on the value of the mass of the objects
orbiting HR8799. An age around 1 Gyr implies that these objects are
brown dwarfs.Comment: 5 pages, 3 figures, accepted in MNRAS Letter
The TELE-DD project on treatment nonadherence in the population with type 2 diabetes and comorbid depression
Diabetic patients have increased depression rates, diminished quality of life, and higher death rates due to depression comorbidity or diabetes complications. Treatment adherence (TA) and the maintenance of an adequate and competent self-care are crucial factors to reach optimal glycaemic control and stable quality of life in these patients. In this report, we present the baseline population analyses in phase I of the TELE-DD project, a three-phased population-based study in 23 Health Centres from the Aragonian Health Service Sector II in Zaragoza, Spain. The objectives of the present report are: (1) to determine the point prevalence of T2D and clinical depression comorbidity and treatment nonadherence; (2) to test if HbA1c and LDL-C, as primary DM outcomes, are related to TA in this population; and (3) to test if these DM primary outcomes are associated with TA independently of shared risk factors for DM and depression, and patients’ health behaviours. A population of 7,271 patients with type-2 diabetes and comorbid clinical depression was investigated for inclusion. Individuals with confirmed diagnoses and drug treatment for both illnesses (n = 3340) were included in the current phase I. A point prevalence of 1.9% was found for the T2D-depression comorbidity. The prevalence of patients nonadherent to treatment for these diseases was 35.4%. Multivariate analyses confirmed that lower diabetes duration, increased yearly PCS visits, HbA1c and LDL-C levels were independently related to treatment nonadherence. These findings informed the development of a telephonic monitoring platform for treatment of nonadherence for people with diabetes and comorbid depression and further trial, cost-effectiveness, and prognostic studies (phases II and III)
The planetary system host HR\,8799: On its Bootis nature
HR\,8799 is a Bootis, Doradus star hosting a planetary
system and a debris disk with two rings. This makes this system a very
interesting target for asteroseismic studies. This work is devoted to the
determination of the internal metallicity of this star, linked with its
Bootis nature (i.e., solar surface abundances of light elements, and
subsolar surface abundances of heavy elements), taking advantage of its
Doradus pulsations. This is the most accurate way to obtain this
information, and this is the first time such a study is performed for a
planetary-system-host star. We have used the equilibrium code CESAM and the
non-adiabatic pulsational code GraCo. We have applied the Frequency Ratio
Method (FRM) and the Time Dependent Convection theory (TDC) to estimate the
mode identification, the Brunt-Va\"is\"al\"a frequency integral and the mode
instability, making the selection of the possible models. When the
non-seismological constraints (i.e its position in the HR diagram) are used,
the solar abundance models are discarded. This result contradicts one of the
main hypothesis for explaining the Bootis nature, namely the
accretion/diffusion of gas by a star with solar abundance. Therefore, according
to these results, a revision of this hypothesis is needed. The inclusion of
accurate internal chemical mixing processes seems to be necessary to explain
the peculiar abundances observed in the surface of stars with internal subsolar
metallicities. The use of the asteroseismological constraints, like those
provided by the FRM or the instability analysis, provides a very accurate
determination of the physical characteristics of HR 8799. However, a dependence
of the results on the inclination angle still remains. The determination of
this angle, more accurate multicolour photometric observations, and high
resolution spectroscopy can definitively fix the mass and metallicity of this
star.Comment: 11 pages, 10 figures. Accepted for publication in MNRA
The stellar occultation by (319) Leona on 2023 September 13 in preparation for the occultation of Betelgeuse
peer reviewedOn 2023 December 12, the star α Orionis will be occulted by asteroid (319) Leona. This represents an extraordinary and unique opportunity to analyse the brightness distribution of Betelgeuse's photosphere with extreme angular resolution by studying light curves from different points on Earth and at different wavelengths. Here we present observations of another occultation by asteroid Leona, on 2023 September 13, whose goal was to determine Leona's projected shape and size in preparation for the December 12th event and its interpretation. The occultation campaign was highly successful with 25 positive detections from 17 different sites and a near miss. The effective diameter in projected area derived from the positive detections was 66 ± 2 km using an elliptical fit to the instantaneous limb. The body is highly elongated, with dimensions of 79.6 ± 2.2 km × 54.8 ± 1.3 km in its long and short axis, respectively, at occultation time. This result, in combination with dense time series photometry of Leona that we recently obtained, together with archival sparse photometry, allowed us to predict the angular size of the asteroid for the Betelgeuse event and to simulate the expected brightness change. Also, an accurate position coming from the occultation is provided, to improve the orbit of Leona