Post-Baccalaureate:

I worked for two years as an astronomer at the Center for Astrophysics | Harvard and Smithsonian (CfA) working with Dr. David Latham. TESS, the Transiting Exoplanet Survey Satellite, is a NASA satellite that launched in April 2018. TESS searches for planets using the transit method. The transit method in exoplanet science is where we look for a periodic decrease in the light received from a distant star, due to the planet passing in front of the star relative to Earth. In working on TESS, I have contributed in several ways to the mission and grown immensely as a researcher.​​ 

My work on the TESS Mission includes:

  • I am a group lead in the planet vetting process  -- for which I individually vet light curves targeted as planet candidates by the analysis pipelines and lead weekly group vetting sessions where we decide which targets to alert as planet candidates to the public. 

  • I run photometric follow-up observations of TESS Objects of Interest (TOIs) using the 16” Clay Telescope at Harvard University to observe TOIs in the northern hemisphere. I also lead outreach SG1 observing sessions of TOIs with undergraduate students at the Clay Telescope as a part of the Harvard Observing Project.

  • I plan and run spectroscopic follow-up observations of TOIs using TRES on the 1.5 m Tillinghast Reflector at FLWO on Mt. Hopkins, AZ. I also help in analyzing TRES spectroscopy of TESS planet candidates by running SPC to estimate the host star temperature, metallicity, surface gravity, and rotation.

  • I run SPC analysis on TRES spectra of TESS planet candidates, so that candidates for precise radial velocity observations by instruments like HARPS-N can be chosen succesfully.

  • I wrote an MCMC RV code, to help with the RV modeling of TRES spectroscopic observations.

Image Credit: MIT Kavli Institute for Astrophysics and Space Research

I also led a follow-up study of KOI-3278, the first discovered self-lensing binary (Kruse and Agol, 2014). In the paper, we presented independent Einsteinian and Newtonian gravitational models for the system and showed that the respective estimates for the white dwarf mass in KOI-3278 agreed within 5.2%. We also presented a joint Einsteinian and Newtonian model that allowed us to remove white dwarf evolution models and assumptions on the white dwarf mass-radius relation. Doing so provided a model independent test of the mass-radius relation and thus white dwarf structure models. ​​

 

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This year, I have been studying a Kepler sub-Neptune system that exhibits significant TTVs. The TTVs and follow-up radial velocity observations are both consistent with an interior, near 1:2 resonant, and non-transiting warm-Jupiter. I am very excited about this system and its potential implications on the formation of warm-Jupiters. I will be presenting this work with a poster at the AAS meeting in January. 

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Yahalomi, D. A. et al. The Astrophysical Journal, 880, 33 (2019).

We are hopeful that further studies of the white dwarf in KOI-3278, as well as four other discovered white dwarf self-lensing systems, in conjunction with UV follow-up observations will provide a test of white dwarf structure models. For more on our work on KOI-3278, see the links below:

Undergraduate at MIT:

As an undergraduate at MIT, I led an investigation into the micro-lensing of the first discovered, strongly lensed type Ia supernova, iPTF16geu. This system cause commotion when it was discovered, as its standard candle nature plus time delay values, could theoretically lead to a constraint of the Hubble parameter. However, the macro-models published by More et al. 2017 showed significant flux ratio anomolies with the observations of the four images. I constructed a Monte-Carlo simulation, in Python, which showed that the likelihood for micro-lensing to cause these flux ratio anomalies between observations and macro-models was ~3/1000. I then showed that even if the macro-models fit perfectly, the microlensing probability density functions create a probability distribution on the intrinsic brightness with a full width half maximum of 0.73 magnitudes. As such, the error for the standard candle brightness is quite large. This reduces the utility of the standard candle nature of type Ia supernovae. This project led to a first author paper, and cover article, in the MIT Undergraduate Research Journal Fall 2017, which has 10 academic citations (as of November 2019). I then built on this work, leading three other micro-lensing projects that took advantage of the code that I had generated, culminating in my senior thesis, entitled “Statistical Analyses of Gravitational Microlensing Probability Densities.”

Yahalomi, D. A., Schechter, P. L, and Wambsganss, J. MURJ, Fall 2017 - arXiv: 1711.07919

 

Demonstrates the effects of microlensing on iPTF16geu. The top left image is taken from More et al., 2017, and is an HST image (F814W) of iPTF16geu. The image titled "Idealized Observation" is our recreation of this image, taking each image to be Gaussian. The image titled "More et al. Model" is our recreation of the More et al., 2017 macro-predictions. Then, nine random microlensing values were determined for each lensed image, using the Monte Carlo model. The random microlensings were then added to the More et al., 2017 macro-model flux values. This demonstrates the significant difference in individual image brightness that microlensing can cause.

Yahalomi, D. A., Schechter, P. L, and Wambsganss, J. MURJ, Fall 2017 - arXiv: 1711.07919

Micro-magnification probability densities with 50% stellar contribution to convergence for the four images of iPTF16geu in the top panel. The four probability densities have all been shifted such that the point of zero micro magnification corresponds to the difference between the observed and macro predicted flux values. By multiplying the four shifted probability densities, we create a plot that represents the likelihood for microlensing to cause the flux ratio anomalies between observations and macro-predictions as a function of the intrinsic magnitude of the source (bottom panel).

For more on my work on iPTF16geu, see the links below:

Daniel Alexander Yahalomi

November 2019