My research is focused on the formation and evolution of planetary systems. I study gas and dust in systems at different evolutionary stages using telescopes covering from radio to optical wavelengths. My research consists of systematic studies of large samples to derive statistical properties at different evolutionary stages (from protoplanetary to debris disk), as well as in-depth imaging studies of individual sources. I am also leading several studies in the rapidly growing field of episodic accretion in FU/EXor sources, aimed at understanding what drives this important phase of star and planet formation. \\ .

The very high incidence of extrasolar planets (Howard, 2013; Burke et al. 2015) implies that most circumstellar disks actually form planetary systems. Studying the structure and evolution of full populations of protoplanetary disks can thus place important constraints on the conditions, timescales, and mechanisms associated with the planet formation process. The Ophiuchus Disk Survey Employing ALMA (ODISEA) is a Band-6 continuum and line imaging survey aimed at studying both the gas and dust components of the entire population of disks at 30~au resolution. Its general goal is to carry out a complete and unbiased demographic study of the disks in Ophiuchus to investigate disk evolution and the planet-formation potential of the entire cloud. In Cieza et al. (2019) we describe the project and present the main results. In Williams et al (2019) we study the mass distribution of the different classes. We have recently submitted a third paper presenting the results from ALMA long-baseline observations at 3-5 au resolution of the 10 brightest targets of the ODISEA project (Figure 1).

Location of the ODISEA (blue frames) and DSHARP (red frames) long-baseline targets in the L1688 star-forming cluster. The locations are overlaid over a 0.6 deg x 0.6 deg color composite from Spitzer 3.6, 4.5, and 8.0 um data. The location of HD~147889, the brightest UV source in the region, is also indicated..

Most young stars undergo repeated short-lived increases in accretion rate (up to several orders of magnitude compared to the quiescent phase), and may correspond to one of the key mechanism for depositing material onto the star. The triggering mechanisms of the outburst are still unknown. My pioneering article on ALMA observations of FU Ori itself (Hales et. al. 2015), was the first of a series of papers on ALMA observations of these types of objects by our group, which correspond to the first systematic ALMA study of episodic accretion objects (Cieza et al. 2016, Ruiz-Rodriguez et al. 2017a, 2017b; Zurlo et al. 2017; Principe at al. 2018; ; Cieza el al. 2018; Hales et al. 2018, Perez et al. 2020; Hales et al. 2020). We have discovered that most disks are compact in continuum, exhibit complex velocity fields, and hold large reservoirs of molecular gas. We found that eruptive stars of the FUor class show wide-angle outflows (wider than typical Class I objects), while eruptive stars of the EXor class do not show these outflows (Figure 2). The detection of wide-angle outflows in FUors but not in EXors supports the current picture in which FUors are more likely to represent an accretion burst in the protostellar phase (Class I), while EXors are smaller accretion events in the protoplanetary (Class II) phase. We reported recently the discovery of an accretion streamer on the prototype outbusrting star, FU~Orionis.

Gallery of eruptive sources observed by ALMA (70% of these targets have been observed by our group).

Comets in the young Solar System played a key role in the delivery of volatiles, including water, into the Earth's young atmosphere. At least 4 debris disk systems, including the archetype beta Pic, exhibit confirmed evidence for gas production via cometary activity. Models of their gas can provide important clues on the volatile composition of exocomets, and by inference on the atmospheres of the exoplanets they will enrich. The archetype $\beta$ Pictoris debris stands out as the best-studied debris disk system with exocometary gas. We have developed a model that can consistently explain its low gas mass and dust luminosities in the frame of colliding volatile-rich bodies. Can this model explain the origin of gas found in other debris disk systems? In Lieman-Sifry et al. 2016 we discoverd gas around several young debris disk systems. In Hales et al. (2019) we applied thermochemical models to the brightest disks in the sample to test both primordial and cometary scenarios for the origin of the gas. Our analysis favors a secondary origin for the gas in these disks and finds that the CO gas masses require production rates similar to those estimated for the bona fide gas-rich debris disk beta Pic. We have recently discovered a young debris disk, that harbors beta Pic-like amounts of dust and gas in mm emission, as well as variable circumstellar absorption in the optical (Hales et al. 2017), strongly suggesting that exocometary activity is ongoing. We acquired Band 6 & 7 ALMA (PI Hales) images of the dust and gas at 0.3 arcsec resolution to obtain key diagnostics to constrain the general case of the exocometary origin of the gas. The disk is detected in continuum and CO isotopologues, analysis and modeling of the disk are presented in Hales et al. 2022.