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Paula Sánchez Sáez, PhD


User Support Astronomer at ESO-Garching.

Member of the ALeRCE broker

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Welcome to my personal webpage!

About me:

I am a Chilean astronomer from Santiago de Chile. In 2019, I obtained my Ph.D. in Astronomy at Universidad de Chile. Between 2019 and 2021, I was a Postdoctoral Fellow at the Millennium Institute for Astrophysics (MAS); then, in November 2021, I moved to Garching, Germany, to work as a Fellow at the European Southern Observatory (ESO). Since March 2024, I work as a User Support Astronomer at ESO. I am also a member of the ALeRCE broker, one of the official brokers for the Vera C. Rubin Observatory legacy survey of space and time (LSST). My main research interests are the study of transients and variable objects in the universe, particularly Active Galactic Nuclei (AGN), and the application of statistical and machine learning techniques to astronomical data sets.

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ESO Fellow

User Support Astronomer

March 2024 - present

European Southern Observatory (ESO-Garching)

Assistant Astronomer

50% independent research, 50% functional work.

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ESO Fellow

November 2021- February 2024

European Southern Observatory (ESO-Garching)

75% independent research, 25% functional work

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April 2020 -  October 2021

Millenium Institute of Astrophysics 

Pontificia Universidad Católica

Project: AGN variability studies in the context of the ALeRCE project

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Postdoctoral Researcher

December 2020 - August 2021

Inria Chile

ALeRCE Broker collaboration with Inria Chile

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Postdoctoral Researcher

May 2019 - April 2020

Millenium Institute of Astrophysics 

Pontificia Universidad Católica

Working on the ALeRCE project.

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PhD Student

March 2013 - April 2019

Universidad de Chile

Thesis: “AGN variability in the era of Big Data”

 Advisor: Dr. Paulina Lira.

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ESO Studentship Programme Chile

April 2018 - March 2019

European Southern Observatory (ESO)

Project: AGN Reverberation Mapping.

Working with Dr. Konrad Tristram

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Visitor Student

January 2017 -  June 2017

Kavli Institute for Astronomy and Astrophysics (KIAA), Beijing, China.

Working with Dr. Luis Ho. 

Penn State University (PSU), State College, USA.  

Working with Dr. Niel Brandt


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Research Projects

Captura de Pantalla 2020-10-03 a la(s) 1
Captura de Pantalla 2020-10-03 a la(s) 1

AGN variability with UltraVISTA

I performed a statistical study of near Infrared (NIR) variability of X-ray-selected AGN in the COSMOS field, using UltraVISTA data. The results of this analysis showed that BL AGN have a considerably larger fraction of variable sources than NL AGN, and that they had different distributions of the amplitude of the variability. The results of this analysis were published in Sánchez et al. (2017). In addition, I am using UltraVISTA data to perform a Reverberation Mapping (RM) analysis of AGN light curves. RM is a valuable technique for investigating the spatially-unresolved structures of AGN, such as the dusty torus. RM measures the observed time lags between contemporaneous light curves of AGN observed in different bands and associates these lags with light travel times between the different structures of the AGN, since different wavelengths map different regions of the system. In particular, I am studying whether the emission received in the NIR is consistent with emission from the dusty torus or the accretion disk and I am determining the characteristic optical-NIR time lags for nine sources.

The QUEST-La Silla AGN Variability Survey

Between 2010 and 2015, a precursor survey to ZTF and LSST called the “The QUEST–La Silla AGN variability survey” (QUEST–La Silla) was carried out, using the wide-field QUEST camera on the 1m ESO-Schmidt telescope at La Silla Observatory (Cartier et al., 2015). The survey targetted the COSMOS, ECDF–S, ELAIS–S1, XMM–LSS and Stripe–82 fields, which were chosen because of the wealth of ancillary data available. I used data from this survey to study the connection between AGN optical variability and SMBH physical properties (Sánchez-Sáez et al., 2018). In addition, I developed a variability–based AGN selection technique to find AGN populations missed by static optical selection techniques (Sánchez-Sáez et al., 2019).

The ALeRCE broker Light Curve Classifier

ALeRCE is currently processing the Zwicky Transient Facility (ZTF) alert stream, in preparation for the Vera C. Rubin Observatory. The ALeRCE light curve classifier (Sánchez-Sáez et al 2020) uses variability features computed from the ZTF alert stream, and colors obtained from AllWISE and ZTF photometry. We apply a Balanced Random Forest algorithm with a two-level scheme, where the top level classifies each source as periodic, stochastic, or transient, and the bottom level further resolves each of these hierarchical classes, amongst 15 total classes. This classifier corresponds to the first attempt to classify multiple classes of stochastic variables (including nucleus- and host-dominated active galactic nuclei, blazars, young stellar objects, and cataclysmic variables) in addition to different classes of periodic and transient sources, using real data.

AGN variability studies in the context of the ALeRCE project

ALeRCE (Automatic Learning for the Rapid Classification of Events; Förster et al., 2020) is an initiative led by an interdisciplinary and inter-institutional group of scientists from the Millennium Institute for Astrophysics (MAS) that aims to facilitate the study of variable and transient objects. ALeRCE is currently processing the ZTF alert stream, providing classifications of different variable and transient objects, in preparation for the upcoming LSST.

In this project I am working on variability studies of AGN, in the context of the ALeRCE project, applying state–of-the–art statistical and computing tools. The main goals of this project are: a) Develop a variability– based classifier that can separate different AGN populations; b) Develop a statistical technique to detect CSAGN, as the transition is happening; c) Develop a variability–based classifier that can detect IMBHs candidates; and d) Search for a connection between the timescale of the variability and the mass of the SMBHs.

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Teaching and Outreach

I have organized and participated in different scientific and outreach activities, like hackathons, workshops, conferences, and public talks.
I worked as a visitor’s guide at the National Astronomical Observatory in Chile, and participated in the "Cazadora de Estrellas" program. 
I have been a professor in the "PENTA UC" program, where I have taught high school students about astronomy and programming using Python. I have been professor of introductory courses in Astronomy at Universidad de los Andes. Besides, I have been an assistant professor of undergraduate and postgraduate courses in astronomy, at Universidad de Chile and Universidad Nacional Andres Bello.
I have also been involved in the organization of conferences like the
“TORUS 2018 conference”, and the two versions of the “Workshop de estudiantes de Astronomía” in Chile.

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Contact Me

European Southern Observatory (ESO)
Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany

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