Christian Flores

Bio

I currently reside in Taipei, Taiwan, working as a Postdoctoral Researcher at the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA). At ASIAA, I collaborate mainly with Nagayoshi Ohashi and Sienny Shang, focusing on ALMA observations of protostellar sources. I earned my PhD from the University of Hawaii at Manoa, where my work was supervised by Michael Connelley and Bo Reipurth. During this period, I also collaborated with Jonathan Williams and Adwin Boogert on shorter-term research projects.

I consider myself an active person who enjoys playing sports, trying new things, and constantly learning. I have enjoyed activities such as salsa and bachata dancing, learning Mandarin Chinese, snorkeling, and contact sports like Taekwondo and Kick Boxing. I also have a passion for teaching, with many years of experience as a physics and math instructor. I have even attempted teaching Latin dance classes.

My interest in science and astronomy began in high school. The mysteries of the universe fascinated me, and I believed uncovering them was an extraordinary endeavor. Initially, the math and physics behind these phenomena captivated me the most. However, during my PhD I developed a significant interest in the beauty of observational astronomy.

Research

My research interest are mainly star and planet formation. I would like to understand the effects of magnetic fields in low-mass young stars and how the star and the disk affect each other at the earliest stages of planet formation.

Star formation and evolution

Stars younger than 1 Myr old, often referred to as protostars, are typically embedded within their birth material, making them accessible primarily through IR observations. I am interested in characterizing their stellar properties, such as temperature and gravity. This helps indirectly determine their masses and age, which in turn, allow us to understand the growth and evolution of young stars.

Magnetic fields

Magnetic fields are fundamentally important in the formation and evolution of stars, but they are often poorly understood and characterized. I perform measurements of magnetic fields in young stars using high-resolution IR spectroscopy through the Zeeman effect. These observations provide insights into how magnetic fields influence the surface and internal structure of young stars. Additionally, the relationship between magnetic fields and stellar properties allows us to investigate the origin of magnetism in stars.

Protoplanetary disks

Protoplanetary disks are the birthsite of planets. They are proven to be highly complex when observed at sufficient spatial resolution which could be itself a signpost of ongoing planet formation. I study the physical properties of these disks using (sub)mm ALMA observations. This enables us to characterize the amount of material in the disks, providing insight into the mass available for planet formation and further stellar growth.

Atmospheric telluric correction

The Earth's atmosphere is opaque at both discrete and continuous wavelengths throughout the electromagnetic spectrum. In the IR wavelength, it is common to observe what are known as A0 telluric standard stars to partially alleviate the discrete flux reduction seen in the observed science spectra. As part of my work at the NASA Infrared Telescope, I helped build a code that produces model spectra of Earth’s transmission. This reduces the need for taking spectra of telluric standard stars. The goal of producing synthetic atmospheric spectra is to increase the observatory's efficiency by collecting more science spectra during the night and performing the subsequent calibrations during the day.

Publications

A list with all my publications can be found in this ADS link. A brief summary of my first author's publications is as follow:

First Author Publications

1. iSHELL K-band Survey of Class I and Flat Spectrum Sources: Magnetic field measurements in the protostellar phase (2024, submitted)


We performed the first magnetic field strength survey of Class I and Flat Spectrum (FS) sources using K-band observations with iSHELL. We model the photospheric absorption lines of 34 Class I and FS sources and measure their magnetic field strengths, K-band temperatures, and gravities. We put the physical properties of Class I and FS sources in context by comparing them to the values derived for a sample of Class II sources. As shown in the image, the average gravity of Class I and FS objects is lower than the average gravity of Class II sources, however, a significant overlap between both gravity distributions exist. Using evolutionary models we show that the average gravity of Class I and FS sources is 0.6 Myrs, significantly younger than the average age of Class II sources of 3 Myrs. Also, the average magnetic field strength of Class I and FS sources 〈B〉 = 1.8 ± 0.10 kG is comparable to the average magnetic field of Class II sources. Our results confirm that protostellar sources host strong magnetic fields on their photospheres and they likely accrete disk material through a magnetosphere similar to their more evolved T Tauri counterparts.

2. Early Planet Formation in Embedded Disks (eDisk). XII. Accretion Streamers, Protoplanetary Disk, and Outflow in the Class I Source Oph IRS 63 (2023 ApJ)


We present ALMA observations of the Class I source Oph IRS63 in the context of the Early Planet Formation in Embedded Disks (eDisk) large program. Our ALMA observations of Oph IRS63 show a myriad of protostellar features, such as a shell-like bipolar outflow (in 12CO), an extended rotating envelope structure (in 13CO), a streamer connecting the envelope to the disk (in C18O), and several small-scale spiral structures seen towards the edge of the dust continuum (in SO). On the left image, I show the beatiful outflow detected in CO, which shows shell-like structures. On the right image, I show a very intriguing spiral and ring-like structure detected in SO.

3. The Effects of Starspots on Spectroscopic Mass Estimates of Low-mass Young Stars (2022 ApJ)


Magnetic fields and mass accretion processes create dark and bright spots on the surface of young stars. These spots manifest as surface thermal inhomogeneities, which alter the global temperature measured on the stars. To understand the effects and implications of these starspots, we conducted a large iSHELL high-resolution infrared spectroscopic survey of T Tauri stars in Taurus-Auriga and Ophiuchus star-forming regions. Our main results are that 1) there is a systematic temperature difference between optical and infrared observation (left panel) and 2) that a positive correlation between our measured magnetic field strengths and the temperature differences (right panel). The discrepant temperature measurements imply significant differences in the inferred stellar masses for these young stars. In this article paper, we use results from ALMA observations to discern which temperature is really tracing the effetive temperature of these largely spotted stars.

4. The Anatomy of an Unusual Edge-on Protoplanetary Disk. II: Gas temperature and a warm outer region (2021 AJ)


We present high-resolution 12CO and 13CO 2 - 1 ALMA observations of the highly-inclined protoplanetary disk around SSTC2D J163131.2-242627. We apply a modified version of the Topographically Reconstructed Distribution method presented by Dutrey et al. (2017) to derive the temperature structure of the disk. CO is clearly detected from two surface layers separated by a midplane region in which CO emission is suppressed, as expected from freeze-out in the cold midplane. Outside of R > 200 au, the midplane temperature of the disk increases with a nearly vertically isotermal profile. The transition in CO temperature coincides in position with a dramatic reduction in the sub-micron and sub-millimeter emission from the disk. We interpret this phenomenon as interstellar UV radiation providing an additional source of heating to the outer part of the disk.

5. Is T Tauri North a "Classical" T Tauri Star? (2020 ApJ)


We present high-resolution H- and K-band spectroscopic observations of the archetypal T Tauri star T Tau North. We find that the IR temperature derived from our work is ~800 K cooler than optical temperature derived in the literatture. This temperature difference is interpreted as cool or hot spots, or both, covering a significant part of the surface of T Tau N. The gravity derived for T Tau N is lower than the gravity of nearly every other star in a sample of 24 classical T Tauri stars in Taurus. Combining these temperature and gravity results with magnetic stellar evolutionary models, we find the age of T Tau N to be less than 1 Myr old. These results suggest that T Tau N is in an earlier evolutionary stage than most classical T Tauri stars in Taurus, arguing that it is a protostar ejected from the embedded southern binary system shortly after its formation.

6. Measuring the Magnetic Field of Young Stars Using iSHELL Observations: BP Tau and V347 Aur (2019 ApJ)


We present stellar parameters and magnetic field strength measurements of BP Tau and V347 Aur, both young stars observed with the near-infrared spectrograph iSHELL. For BP Tau, we measure a surface magnetic field strength of 2.5 kG literature results. For this star, however, we obtain a much lower temperature value than previous optical studies (dT~ 400 K) and interpret this significant temperature difference as due to the relatively higher impact of starspots at near-infrared wavelengths than at optical wavelengths. We further apply this technique to the class I protostellar source V347 Aur and measure for the first time its magnetic field strength of 1.35 kG and its surface gravity log g= 3.25. Lastly, we combine our measurements with pre-main-sequence stellar evolutionary models and illustrate the effects produced by starspots on the retrieved masses and ages of young stars.

Selected co-author Publications

• Early Planet Formation in Embedded Disks (eDisk). I. Overview of the Program and First Results (2023)
• A Highly Settled Disk around Oph163131 (2022)
• The Anatomy of an Unusual Edge-on Protoplanetary Disk I. Dust Settling in a Cold Disk (2021)
• Observations of edge-on protoplanetary disks with ALMA I. Results from continuum data (2020)
• Upper limits on protolunar disc masses using ALMA observations of directly imaged exoplanets (2019)
• Characterization of low-mass companion HD 142527 B (2018)
• Planet Formation Signposts: Observability of Circumplanetary Disks via Gas Kinematics (2015)

Non-refereed Publications

• Telluric Correction of IRTF Spectra with Atmospheric Models
• On the edge: Assessing the structure of protoplanetary disks from a unique perspective
• Gas and dust in an edge-on protoplanetary disk: An in-depth multiwavelength analysis

Christian's Resume

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