Constraining the Variability and Binary Fraction of Galactic Center Young Stars

We present constraints on the variability and binarity of young stars in the central 10 arcseconds (~0.4 pc) of the Milky Way Galactic Center (GC) using Keck Adaptive Optics data over a 12 year baseline. Given our experiment's photometric uncertainties, at least 36% of our sample's known early-type stars are variable. We identified eclipsing binary systems by searching for periodic variability. In our sample of spectroscopically confirmed and likely early-type stars, we detected the two previously discovered GC eclipsing binary systems. We derived the likely binary fraction of main sequence, early-type stars at the GC via Monte Carlo simulations of eclipsing binary systems, and find that it is at least 32% with 90% confidence.Comment: Accepted for publication in Proceedings of IAU Symposium 322: The Multi-Messenger Astrophysics of the Galactic Centre, 2 pages, 1 figur

Unprecedented Near-infrared Brightness and Variability of Sgr A*

The electromagnetic counterpart to the Galactic center supermassive black hole, Sgr A*, has been observed in the near-infrared for over 20 yr and is known to be highly variable. We report new Keck Telescope observations showing that Sgr A* reached much brighter flux levels in 2019 than ever measured at near-infrared wavelengths. In the K' band, Sgr A* reached flux levels of ~6 mJy, twice the level of the previously observed peak flux from >13,000 measurements over 130 nights with the Very Large Telescope and Keck Telescopes. We also observe a factor of 75 change in flux over a 2 hr time span with no obvious color changes between 1.6 and 2.1 μm. The distribution of flux variations observed this year is also significantly different than the historical distribution. Using the most comprehensive statistical model published, the probability of a single night exhibiting peak flux levels observed this year, given historical Keck observations, is less than 0.3%. The probability of observing flux levels that are similar to all four nights of data in 2019 is less than 0.05%. This increase in brightness and variability may indicate a period of heightened activity from Sgr A* or a change in its accretion state. It may also indicate that the current model is not sufficient to model Sgr A* at high flux levels and should be updated. Potential physical origins of Sgr A*'s unprecedented brightness may be from changes in the accretion flow as a result of the star S0-2's closest passage to the black hole in 2018, or from a delayed reaction to the approach of the dusty object G2 in 2014. Additional multi-wavelength observations will be necessary to both monitor Sgr A* for potential state changes and to constrain the physical processes responsible for its current variability

The Galactic Center with Roman

We advocate for a Galactic center (GC) field to be added to the Galactic Bulge Time Domain Survey (GBTDS). The new field would yield high-cadence photometric and astrometric measurements of an unprecedented ${\sim}$3.3 million stars toward the GC. This would enable a wide range of science cases, such as finding star-compact object binaries that may ultimately merge as LISA-detectable gravitational wave sources, constraining the mass function of stars and compact objects in different environments, detecting populations of microlensing and transiting exoplanets, studying stellar flares and variability in young and old stars, and monitoring accretion onto the central supermassive black hole. In addition, high-precision proper motions and parallaxes would open a new window into the large-scale dynamics of stellar populations at the GC, yielding insights into the formation and evolution of galactic nuclei and their co-evolution with the growth of the supermassive black hole. We discuss the possible trade-offs between the notional GBTDS and the addition of a GC field with either an optimal or minimal cadence. Ultimately, the addition of a GC field to the GBTDS would dramatically increase the science return of Roman and provide a legacy dataset to study the mid-plane and innermost regions of our Galaxy.Comment: 19 pages, 3 figures. Submitted to the NASA Roman Core Community Surveys White Paper Cal

abhimat/binary_fraction: binary_fraction v1.0.0

Binary fraction software finalized as a python package for initial ApJ submission of the Gautam et al. (2023) pape

abhimat/phitter: Phitter v0.1.0

Initial pre-release of Phitter. More work in documentation and package structure is required to have this set up and released as a full python package

The Effect of Desire on Identity in the Harry Potter novels. Deleuze and Guattari Against Psychoanalysis

Tutkielmassani käsittelen J. K. Rowlingin Harry Potter -romaanisarjaa psykoanalyysin, etupäässä Sigmund Freudin ja Jacques Lacanin, sekä jälkistrukturalististen Gilles Deleuzen ja Félix Guattarin teorioiden valossa. Tarkemmin tutkimuskohteenani ovat eri henkilöhahmojen halut sekä niiden suhteet ja vaikutus kunkin identiteettiin ja sen muotoutumiseen. Lähden siitä oletuksesta, että paljon käytetyt psykoanalyyttiset teoriat eivät yksinään riitä kattavaan syvälliseen kuvaukseen näistä aiheista, minkä vuoksi annan Deleuzen ja Guattarin teorialle etusijan tulkinnoissani. Aloitan määrittelemällä oman sijoittumiseni Harry Potter -tutkimuksen kentässä ja esittelemällä lyhyesti eri tutkijoiden käsityksiä halusta ja identiteetistä. Tutkimukseni painotuksen vuoksi teoriaosuuteen sisältyy myös Deleuzen ja Guattarin esittämää kritiikkiä psykoanalyysin näkemyksiä kohtaan. Pääpaino on tekstin analyysillä: suurin huomio kohdistuu romaanien päähenkilön Harry Potterin haluihin ja toiveisiin hänen identiteettinsä kehittymisen osina. Näihin palaan useassa kappaleessa joko yksittäisinä esimerkkeinä tai toiseen henkilöhahmoon liittyen. Myös sarjan muut hahmot tuovat esiin ja käsittelevät haluja erilaisin tavoin, ja olen pyrkinyt jakamaan analyysiosan luvut pääotsikoilla näiden tapojen mukaan. Eräs tulkintani avainkäsitteistä on Deleuzen ja Guattarin käyttämä rihmasto, jota he soveltavat biologian alalta yhteiskuntaan. Hyödynnän tätä määritelmää monessa yhteydessä kuvaillessani romaaneissa kasvussa olevaa (mikro)yhteiskuntarakennetta; vastakohtana tulee esiin hierarkkinen yhteiskuntarakenne. Johtopäätöksissäni korostan kuitenkin sitä lopputulosta, ettei mikään näistä teorioista yksin selitä täydellisen uskottavasti tutkimusongelmiani. Niistä yhdessä muodostuu silti kokonaisuus, jonka osat tuottavat vuorovaikutuksessa keskenään rakentavia kuvaus- ja arviointitapoja. Mitä yksittäisiin henkilöhahmoihin tulee, heidän haluillaan vaikuttaa usein olevan samanlainen pohjavire, jota voi myös kutsua Deleuzen ja Guattarin esimerkin mukaan halun virtaukseksi. Halu liittyy tavalla tai toisella lähes jokaisella hahmolla sosiaalisiin tavoitteisiin ja motivaatioon, mutta tavat pyrkiä saavuttamaan haluamansa vaihtelevat suuresti, samoin kuin se, mikä kutakin heistä motivoi. Lisäksi kiinnitän johtopäätöksissä huomiota kysymyksiin, jotka jatkuvasti kulkevat romaanisarjassa tapahtumien taustalla. Tällainen on epäily siitä, onko ensinkään hyvä saada haluamansa ­ lähes aina halu päätyy turhautumiseen tai vaikeuksiin. Tähän liittyy myös halujen näkeminen ”hyvinä” tai ”pahoina” siinä merkityksessä kuin hyvän ja pahan vastakkainasettelu esiintyy fantasiakirjallisuudessa. Avainsanat: desire, identity, Deleuze and Guattari, rhizom

Near-infrared Flux Distribution of Sgr A* from 2005–2022: Evidence for an Enhanced Accretion Episode in 2019

Sgr A* is the variable electromagnetic source associated with accretion onto the Galactic center supermassive black hole. While the near-infrared (NIR) variability of Sgr A* was shown to be consistent over two decades, unprecedented activity in 2019 challenges existing statistical models. We investigate the origin of this activity by recalibrating and reanalyzing all of our Keck Observatory Sgr A* imaging observations from 2005–2022. We present light curves from 69 observation epochs using the NIRC2 imager at 2.12 μ m with laser-guide star adaptive optics. These observations reveal that the mean luminosity of Sgr A* increased by a factor of ∼3 in 2019, and the 2019 light curves had higher variance than in all time periods we examined. We find that the 2020–2022 flux distribution is statistically consistent with the historical sample and model predictions, but with fewer bright measurements above 0.6 mJy at the ∼2 σ level. Since 2019, we have observed a maximum K _s (2.2 μ m) flux of 0.9 mJy, compared to the highest pre-2019 flux of 2.0 mJy and highest 2019 flux of 5.6 mJy. Our results suggest that the 2019 activity was caused by a temporary accretion increase onto Sgr A*, possibly due to delayed accretion of tidally stripped gas from the gaseous object G2 in 2014. We also examine faint Sgr A* fluxes over a long time baseline to search for a quasi-steady quiescent state. We find that Sgr A* displays flux variations over a factor of ∼500, with no evidence for a quiescent state in the NIR

Relativistic redshift of the star S0-2 orbiting the Galactic Center supermassive black hole.

The general theory of relativity predicts that a star passing close to a supermassive black hole should exhibit a relativistic redshift. In this study, we used observations of the Galactic Center star S0-2 to test this prediction. We combined existing spectroscopic and astrometric measurements from 1995-2017, which cover S0-2's 16-year orbit, with measurements from March to September 2018, which cover three events during S0-2's closest approach to the black hole. We detected a combination of special relativistic and gravitational redshift, quantified using the redshift parameter ϒ. Our result, ϒ = 0.88 ± 0.17, is consistent with general relativity (ϒ = 1) and excludes a Newtonian model (ϒ = 0) with a statistical significance of 5σ