Francesc Vilardell

First Determination of the Distance and Fundamental Properties of an Eclipsing Binary in the Andromeda Galaxy

We present the first detailed spectroscopic and photometric analysis of an eclipsing binary in the Andromeda Galaxy (M31). This is a 19.3 mag semidetached system with late O and early B spectral type components. From the light and radial velocity curves we have carried out an accurate determination of the masses and radii of the components. Their effective temperatures have been estimated by modeling the absorption-line spectra. The analysis yields an essentially complete picture of the properties of the system, and hence an accurate distance determination to M31. The result is d = 772 ± 44 kpc [(m - M)0 = 24.44 ± 0.12 mag]. The study of additional systems, currently in progress, should reduce the uncertainty of the M31 distance to better than 5%.

The distance to the Andromeda galaxy from eclipsing binaries

The cosmic distance scale largely depends on distance determinations to galaxies of the Local Group. In this sense, the Andromeda galaxy (M 31) is a key rung to better constrain the cosmic distance ladder. A project was started in 1999 to firmly establish a direct and accurate distance to M 31 using eclipsing binaries (EBs). After the determination of the first direct distance to M 31 from EBs, the second direct distance to an EB system is presented: M31V J00443610+4129194. Light and radial velocity curves were obtained and fitted to derive the masses and radii of the components. The acquired spectra were combined and disentangled to determine the temperature of the components. The analysis of the studied EB resulted in a distance determination to M 31 of (m − M)0 = 24.30 ± 0.11 mag. This result, when combined with the previous distance determination to M 31, results in a distance modulus of (m − M)0 = 24.36 ± 0.08 mag (744 ± 33 kpc), fully compatible with other distance determinations to M 31. With an error of only 4%, the obtained value firmly establishes the distance to this important galaxy and represents the fulfillment of the main goal of our project.

Eclipsing binaries suitable for distance determination in the Andromeda galaxy

The Local Group galaxies constitute a fundamental step in the definition of cosmic distance scale. Therefore, obtaining accurate distance determinations to the galaxies in the Local Group, and notably to the Andromeda Galaxy (M31), is essential to determining the age and evolution of the Universe. With this ultimate goal in mind, we started a project to use eclipsing binaries as distance ind icators to M31. Eclipsing binaries have been proved to yield direct and precise distances that are essentially assumption free. To do so, high-quality photometric and spectroscopic data are needed. As a first step in the project, broad band photometry (in Johnson B and V) has been obtained in a region (34 ′ ×34 ′ ) at the North‐Eastern quadrant of the galaxy over 5 years. The data, containing more than 250 observations per filter, have been reduced by means of the so-called difference image analysis technique and the DAOPHOT program. A catalog with 236 238 objects with photometry in both B and V passbands has been obtained. The catalog is the deepest (V< 25.5 mag) obtained so far in the studied region and contains 3 964 identified variable stars, with 437 eclipsing binaries and 4 16 Cepheids. The most suitable eclipsing binary candidates for distance determination have been selected according to their brightness and from the modelling of the obtained light curves. The resulting sample includes 24 targets with photometric errors around 0.01 mag. Detailed analysis (including spectroscopy) of some 5‐10 of these eclipsing systems should result in a distance determination to M31 with a relative uncertainty of 2‐3% and essentially free from systematic errors, thus representing the most accurate and reliable determination to date.

A comprehensive study of Cepheid variables in the Andromeda galaxy - Period distribution, blending, and distance determination

Extragalactic Cepheids are the basic rungs of the cosmic distance scale. They are excellent standard candles, although their luminosities and corresponding distance estimates can be affected by the particular properties of the host galaxy. Therefore, the accurate analysis of the Cepheid population in other galaxies, and notably in the Andromeda galaxy (M 31), is crucial to obtaining reliable distance determinations. We obtained accurate photometry (in B and V passbands) of 416 Cepheids in M 31 over a five year campaign within a survey aimed at the detection of eclipsing binaries. The resulting Cepheid sample is the most complete in M 31 and has almost the same period distribution as the David Dunlap Observatory sample in the Milky Way. The large number of epochs (∼250 per filter) has permitted the characterisation of the pulsation modes of 356 Cepheids, with 281 of them pulsating in the fundamental mode and 75 in the first overtone. The period-luminosity relationship of the fundamental mode Cepheids has been studied and a new approach has been used to estimate the effect of blending. We find that the blending contribution is as important as the metallicity correction when computing Cepheid distance determinations to M 31 (∼0.1 mag). Since large amplitude Cepheids are less affected by blending, we have used those with an amplitude AV > 0.8 mag to derive a distance to M 31 of (m − M)0 = 24.32 ± 0.12 mag.

STARS: framework for scheduling telescopes and space missions like CARMENES, TJO and ARIEL-ESA (Conference Presentation)

Efficient scheduling of astronomical surveys is a challenge with an increasing level of complexity as the observation strategies are becoming more sophisticated and operational costs are higher. In general, any kind of astronomical survey requires the execution of a huge number of observations fulfilling several constraints. The fulfillment and optimization of these constraints is a key factor for obtaining an efficient schedule with an adequate exploitation of the resources and with a high scientific return. In this contribution, we present the framework STARS (Scheduling Telescopes as Autonomous Robotic Systems) that computes optimal schedules for a variety of space- and ground-based infrastructures and scientific exploitation plans. STARS provides methods, tools and libraries for the definition of surveys (e.g., objects to observe, features of the objects, observation constraints), the definition of the observatories (e.g., location, number of telescopes, type of telescopes, sub-array configurations), the usage of astronomical calculations (e.g., object coordinates, object elevation, Sun and Moon position, Moon phase), and the application of schedulers (e.g., long-term, short-term) based on Genetic Algorithms (GAs) and astronomy-based heuristics. In STARS, two main types of schedulers are defined: long-term and short-term. The long-term scheduler is focused on scheduling object observations with a time scope ranging from one night to several months or years. It considers the observation constraints (hard-constraints) that can be predicted beforehand, and it optimizes some objectives (soft constraints) by using GAs. The execution of the long-term scheduler can be time-expensive, but it is not time-critical because it can be run before the start of the telescope operation, so it can be used as a standalone scheduling tool. On the other hand, the short-term scheduler computes in real-time the next observation (or scheduling block) to be executed by optimizing some soft constraints, fulfilling all the hard constraints and by considering all the observations previously executed. The short-term scheduler is time-critical and reacts in less than a second to the changing conditions (weather, errors, delays, targets of opportunity). It uses astronomy-based heuristics to repair the schedule obtained by the long-term scheduler, in order to keep the long-term perspective while avoiding intensive calculations. STARS has been successfully applied in several ground and space-based observatories. It is used to operate the CARMENES instrument (Calar Alto, carmenes.caha.es) and the Joan Oro robotic Telescope (www.oadm.cat). It is used to prototype the mission planning tool for the ARIEL M4-ESA candidate mission, and in prototypes for large ground-based installations, such i.e. the Cherenkov Telescope Array (CTA). Finally, STARS is also being extended to cover multi-observatory coordinated scheduling purposes, under the framework of the EU-H2020 ASTERICS project, and in order to promote multi-messenger science. The coordination of large observatories in the northern and southern hemispheres are used as test cases to evaluate the performance of such an innovative scheduling solution. In this sense, simultaneous observations or minimal time gap between observations are promoted resulting in a challenging and complex optimization problem that will open a new era for the optimal operation of large astrophysical infrastructures.

Using Robotic Operating System (ROS) to control autonomous observatories

Astronomical observatories are complex systems requiring the integration of numerous devices into a common platform. We are presenting here the firsts steps to integrate the popular Robotic Operating System (ROS) into the control of a fully autonomous observatory. The observatory is also equipped with a decision-making procedure that can automatically react to a changing environment (like weather events). The results obtained so far have shown that the automation of a small observatory can be greatly simplified when using ROS, as well as robust, with the implementation of our decision-making algorithms.

Distance Determination to the Andromeda Galaxy Using Variable Stars

Distance determinations to Local Group galaxies conform the basic rungs of the cosmological distance scale. The chief goal of our project is obtaining direct and accurate distance determinations to M 31 from two important stellar populations: eclipsing binaries and Cepheids. A variability survey in the North–Eastern quadrant of M 31 was performed (in B and V passbands) with the Isaac Newton Telescope (La Palma) to identify suitable targets. The resulting catalog of 3,964 variable stars contains 437 eclipsing binaries and 416 Cepheids with ∼ 250 epochs per filter. The selection of the 68 Cepheids less affected by blending were selected to determine a distance to M 31 of (m − M)0 = 24. 32 ± 0. 12 mag. At the same time, the analysis of the eclipsing binary sample (with the acquisition of Gemini/GMOS spectroscopy) has provided two direct distance determinations to M 31: (m − M)0 = 24. 44 ± 0. 12 mag and (m − M)0 = 24. 46 ± 0. 19 mag. All the obtained distances are in complete agreement and provide a direct and accurate distance determination to M 31. The combination of these results with additional data could well reduce the distance uncertainty to M 31 to better than 4%.

A Direct and Accurate Distance to M31 from Eclipsing Binaries

The Andromeda Galaxy (M31), with its large and diverse stellar population and chemical history and galactic structure similar to that of the Milky Way, is potentially a crucial calibrator for the Cosmic Distance Scale and thus for determining the age and evolution of the Universe. We have demonstrated in our work on the LMC distance that double-line eclipsing binaries can serve as excellent “standard candles”. Also, the resulting accurate fundamental properties (M, R, T eff) of the two binary components yield an empirical determination of the mass-luminosity law and permit critical tests of stellar structure and evolution models.