M. A. Agueros - Columbia University

M. A. Agueros
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Name
M. A. Agueros
Affiliation
Columbia University
City
New York
Country
United States

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Solar and Stellar Astrophysics (25)
 
Astrophysics (12)
 
Instrumentation and Methods for Astrophysics (6)
 
Astrophysics of Galaxies (6)
 
Cosmology and Nongalactic Astrophysics (1)
 
High Energy Astrophysical Phenomena (1)

Publications Authored By M. A. Agueros

We present the results of a spectroscopic survey to characterize chromospheric activity, as measured by H$\alpha$ emission, in low-mass members of the 500-Myr-old open cluster M37. Combining our new measurements of H$\alpha$ luminosities ($L_{H\alpha}$) with previously cataloged stellar properties, we identify saturated and unsaturated regimes in the dependence of the $L_{H\alpha}$-to-bolometric-luminosity ratio, $L_{H\alpha}/L_{bol}$, on the Rossby number $R_o$. All rotators with Ro smaller than 0. Read More

We use a 440.5 ks Chandra observation of the $\approx$500-Myr-old open cluster M37 to derive the X-ray luminosity functions of its $\leq1.2$ $M_{\odot}$ stars. Read More

For sufficiently wide orbital separations {\it a}, the two members of a stellar binary evolve independently. This implies that in a wide double white dwarf (DWD), the more massive WD should always be produced first, when its more massive progenitor ends its main-sequence life, and should therefore be older and cooler than its companion. The bound, wide DWD HS 2220$+$2146 ($a\approx500$ AU) does not conform to this picture: the more massive WD is the younger, hotter of the pair. Read More

We present Chandra and Swift X-ray observations of four extremely low-mass (ELM) white dwarfs with massive companions. We place stringent limits on X-ray emission from all four systems, indicating that neutron star companions are extremely unlikely and that the companions are almost certainly white dwarfs. Given the observed orbital periods and radial velocity amplitudes, the total masses of these binaries are greater than 1. Read More

As the closest open cluster to the Sun, the Hyades is an important benchmark for many stellar properties, but its members are also scattered widely over the sky. Previous studies of stellar rotation in the Hyades relied on targeted observations of single stars or data from shallower all-sky variability surveys. The re-purposed Kepler mission, K2, is the first opportunity to measure rotation periods ($P_{rot}$) for many Hyads simultaneously while also being sensitive to fully convective M dwarf members. Read More

2016Jan
Affiliations: 1Western Washington Univ, 2Columbia Univ, 3Univ. of North Carolina-Chapel Hill, 4Columbia Univ, 5Max Planck Institut for Radioastronomy, 6Spitzer Science Center, 7California Institute of Technology, 8Max Planck Institute for Astronomy, 9Spitzer Science Center

Stellar rotation periods measured in open clusters have proved to be extremely useful for studying stars' angular momentum content and rotationally driven magnetic activity, which are both age- and mass-dependent processes. While period measurements have been obtained for hundreds of solar-mass members of the Pleiades, period measurements exist for only a few low-mass ($<$0.5 M$_{\odot}$) members of this key laboratory for stellar evolution theory. Read More

We present observational constraints on the initial-final mass relation (IFMR) using wide double white dwarfs (DWDs). We identify 65 new candidate wide DWDs within the Sloan Digital Sky Survey, bringing the number of candidate wide DWDs to 142. We then engage in a spectroscopic follow-up campaign and collect existing spectra for these objects; using these spectra, we derive masses and cooling ages for 54 hydrogen (DA) WDs in DWDs. Read More

Empirical calibrations of the stellar age-rotation-activity relation (ARAR) rely on observations of the co-eval populations of stars in open clusters. We used the Chandra X-ray Observatory to study M37, a 500-Myr-old open cluster that has been extensively surveyed for rotation periods ($P_{\rm rot}$). M37 was observed almost continuously for five days, for a total of 440. Read More

We present parallax observations and a detailed model atmosphere analysis of 54 cool and ultracool ($T_{\rm eff}$ < 4000 K) white dwarfs (WDs) in the solar neighbourhood. For the first time, a large number of cool and ultracool WDs have distance and tangential velocities measurements available. Our targets have distances ranging from 21 pc to >100 pc, and include five stars within 30 pc. Read More

Measuring the masses of companions to single-line spectroscopic binary stars is (in general) not possible because of the unknown orbital plane inclination. Even when the mass of the visible star can be measured, only a lower limit can be placed on the mass of the unseen companion. However, since these inclination angles should be isotropically distributed, for a large enough, unbiased sample, the companion mass distribution can be deconvolved from the distribution of observables. Read More

In wide double white dwarf (DWD) binaries, in which the co-eval WDs evolve independently, the more massive, faster-evolving WD can be used to obtain a main-sequence lifetime for the less-massive WD. By converting this lifetime into an initial mass for the less-massive WD, and combining it with the spectroscopically derived mass for this WD, one can constrain the initial-final mass relation (IFMR). However, the number of known and well-characterized DWDs is small, severely limiting their usefulness for this analysis. Read More

Open clusters are collections of stars with a single, well-determined age, and can be used to investigate the connections between angular-momentum evolution and magnetic activity over a star's lifetime. We present the results of a comparative study of the relationship between stellar rotation and activity in two benchmark open clusters: Praesepe and the Hyades. As they have the same age and roughly solar metallicity, these clusters serve as an ideal laboratory for testing the agreement between theoretical and empirical rotation-activity relations at $\approx$600 Myr. Read More

Many photometric time-domain surveys are driven by specific goals, such as searches for supernovae or transiting exoplanets, which set the cadence with which fields are re-imaged. In the case of the Palomar Transient Factory (PTF), several sub-surveys are conducted in parallel, leading to non-uniform sampling over its $\sim$$20,000 \mathrm{deg}^2$ footprint. While the median $7. Read More

We present optical and X-ray observations of two tidally distorted, extremely low-mass white dwarfs (WDs) with massive companions. There is no evidence of neutron stars in our Chandra and XMM observations of these objects. SDSS J075141. Read More

We present optical spectroscopy, astrometry, radio, and X-ray observations of the runaway binary LP 400-22. We refine the orbital parameters of the system based on our new radial velocity observations. Our parallax data indicate that LP 400-22 is significantly more distant (3 sigma lower limit of 840 pc) than initially predicted. Read More

Wide binaries made up of two white dwarfs (WDs) receive far less attention than their tight counterparts. However, our tests using the binary population synthesis code {\tt StarTrack} indicate that, for any set of reasonable initial conditions, there exists a significant observable population of double white dwarfs (WDWDs) with orbital separations of 10$^2$ to 10$^5$ AU. We adapt the technique of Dhital et al. Read More

We construct a photometrically calibrated catalog of non-variable sources from the Palomar Transient Factory (PTF) observations. The first version of this catalog presented here, the PTF photometric catalog 1.0, contains calibrated R_PTF-filter magnitudes for about 21 million sources brighter than magnitude 19, over an area of about 11233 deg^2. Read More

We present new radial velocity and X-ray observations of extremely low-mass (ELM, 0.2 Msol) white dwarf candidates in the Sloan Digital Sky Survey (SDSS) Data Release 7 area. We identify seven new binary systems with 1-18 h orbital periods. Read More

The Palomar Transient Factory (PTF) provides multiple epoch imaging for a large fraction of the sky. Here we describe the photometric calibration of the PTF data products that relates the PTF magnitudes to other mag systems. The calibration process utilizes SDSS r~16 mag point source objects as photometric standards. Read More

This paper completes the series of cataclysmic variables (CVs) identified from the Sloan Digital Sky Survey I/II. The coordinates, magnitudes and spectra of 33 CVs are presented. Among the 33 are eight systems known previous to SDSS (CT Ser, DO Leo, HK Leo, IR Com, V849 Her, V405 Peg, PG1230+226 and HS0943+1404), as well as nine objects recently found through various photometric surveys. Read More

2011Jul
Affiliations: 1Columbia, 2Cornell, 3Columbia, 4Toronto, 5IfA, 6Cornell, 7Berkeley, 8Berkeley, 9Caltech, 10Caltech, 11LBNL, 12Caltech, 13Berkeley, 14Caltech

Stellar rotation periods measured from single-age populations are critical for investigating how stellar angular momentum content evolves over time, how that evolution depends on mass, and how rotation influences the stellar dynamo and the magnetically heated chromosphere and corona. We report rotation periods for 40 late-K to mid-M stars members of the nearby, rich, intermediate-age (~600 Myr) open cluster Praesepe. These rotation periods were derived from ~200 observations taken by the Palomar Transient Factory of four cluster fields from 2010 February to May. Read More

We report on follow-up observations of candidate X-ray bright, radio-quiet isolated neutron stars (INSs) identified from correlations of the ROSAT All-Sky Survey (RASS) and the Sloan Digital Sky Survey (SDSS) Data Release 4 in Ag\"ueros et al. (2006). We obtained Chandra X-ray Telescope exposures for 13 candidates in order to pinpoint the source of X-ray emission in optically blank RASS error circles. Read More

Over the past 40 years, observational surveys have established the existence of a tight relationship between a star's age, rotation period, and magnetic activity. This age-rotation-activity relation documents the interplay between a star's magnetic dynamo and angular momentum evolution, and provides a valuable age estimator for isolated field stars. While the age-rotation-activity relation has been studied extensively in clusters younger than 500 Myr, empirically measured rotation periods are scarce for older ages. Read More

We describe new radial velocity and X-ray observations of extremely low-mass white dwarfs (ELM WDs, ~0.2 Msol) in the Sloan Digital Sky Survey Data Release 4 and the MMT Hypervelocity Star survey. We identify four new short period binaries, including two merger systems. Read More

During a synoptic survey of the North American Nebula region, the Palomar Transient Factory (PTF) detected an optical outburst (dubbed PTF10nvg) associated with the previously unstudied flat or rising spectrum infrared source IRAS 20496+4354. The PTF R-band light curve reveals that PTF10nvg brightened by more than 5 mag during the current outburst, rising to a peak magnitude of R~13.5 in 2010 Sep. Read More

We measure the radial velocity curve of the eclipsing detached white dwarf binary NLTT 11748. The primary exhibits velocity variations with a semi-amplitude of 273 km/s and an orbital period of 5.641 hr. Read More

2009Jun
Affiliations: 1Columbia U, 2U of Alberta, 3Columbia U, 4CfA, 5U of Washington, 6Arecibo Obs, 7Gemini Obs, 8Steward Obs, 9U of Washington

SDSS J091709.55+463821.8 (hereafter J0917+4638) is the lowest surface gravity white dwarf (WD) currently known, with log g = 5. Read More

2009Apr
Affiliations: 1Columbia University, 2University of Groningen, 3Columbia University, 4Rice University, 5CESR Toulouse, 6Tata Institute of Fundamental Research, Mumbai, 7University of Michigan, 8NASA Goddard Space Flight Center, 9European Space Astronomy Centre, ESA, 10Penn State University, 11Harvard-Smithsonian Center for Astrophysics, 12Columbia University, 13SRON Netherlands Institute for Space Research, 14University of Southampton, 15University of California at Berkeley, 16SRON Netherlands Institute for Space Research, 17NASA Goddard Space Flight Center, 18University of Iowa, 19Penn State University, 20SUNY Stony Brook, 21Universita degli Studi Roma Tre, 22University of Arizona, 23Penn State University, 24McGill University, 25Harvard-Smithsonian Center for Astrophysics, 26Osservatorio Astronomico di Roma, 27NASA Goddard Space Flight Center, 28Harvard-Smithsonian Center for Astrophysics, 29University of Southampton, 30University of Toronto, 31NASA Marshall Space Flight Center, 32Mullard Space Science Laboratory

The cores of neutron stars harbor the highest matter densities known to occur in nature, up to several times the densities in atomic nuclei. Similarly, magnetic field strengths can exceed the strongest fields generated in terrestrial laboratories by ten orders of magnitude. Hyperon-dominated matter, deconfined quark matter, superfluidity, even superconductivity are predicted in neutron stars. Read More

2009Mar
Affiliations: 1NOAO, 2Columbia Univ, 3LCOGT, 4UC, Berkeley, 5Harvard CfA, 6UC, Berkeley, 7Chicago State Univ., 8Univ. of Nottingham, 9Caltech, 10Griffith Obs., 11Univ of Wisconsin, Madison, 12Rutgers Univ., 13NYU, 14Univ. of Florida, 15Univ. of Denver, 16Univ. of Michigan, 17Univ. of Hawaii, 18NCAR, 19UNC, 20UC, Irvine, 21UC, Santa Cruz, 22San Diego State Univ., 23Univ. of Colorado, Boulder, 24Univ. of Amsterdam, 25OCIW, 26Caltech, 27Lehigh University, 28Indiana Univ., 29UC, Irvine, 30CTIO, 31Columbia Univ., 32Texas A&M

The NSF's Astronomy and Astrophysics Postdoctoral Fellowship (AAPF) is exceptional among the available postdoctoral awards in Astronomy and Astrophysics. The fellowship is one of the few that allows postdoctoral researchers to pursue an original research program, of their own design, at the U.S. Read More

2009Mar
Affiliations: 1NOAO, 2AAS, 3Columbia University, 4Columbia University, 5University of Washington, 6Rutgers University, 7Caltech, 8Caltech, 9Vanderbilt University, Pres. of the Nat. Soc. of Hispanic Physicists, 10Rutgers University, 11University ofMaryland, College Park, 12Washington State University, 13NOAO, 14Western Kentucky University, 15University of Notre Dame, 16Spitzer Science Center, 17STScI, 18Princeton University, 19South Carolina State University, 20MIT, 21Faculty Project Leader, 22University of Washington, 23University of Washington, 24University of Washington, 25University of Washington, 26University of Washington, 27University of Washington, 28University of Washington, 29University of Washington, 30University of Washington, 31University of Washington, 32University of Washington, 33University of Washington

Promoting racial and ethnic diversity is critically important to the future success and growth of the field of astronomy. The raw ability, drive and interest required to excel in the field is distributed without regard to race, gender, or socioeconomic background. By not actively promoting diversity in our field we risk losing talented people to other professions (or losing them entirely), which means that there will be astronomical discoveries that simply won't get made. Read More

2009Mar
Affiliations: 1NOAO, 2AAS, 3Columbia University, 4Columbia University, 5University of Washington, 6Rutgers University, 7Caltech, 8Caltech, 9Vanderbilt University, Pres. of the Nat. Soc. of Hispanic Physicists, 10Rutgers University, 11University of Maryland, College Park, 12Washington State University, 13NOAO, 14Western Kentucky University, 15University of Notre Dame, 16Spitzer Science Center, 17STScI, 18Princeton University, 19South Carolina State University, 20MIT, 21Faculty Project Leader, 22University of Washington, 23University of Washington, 24University of Washington, 25University of Washington, 26University of Washington, 27University of Washington, 28University of Washington, 29University of Washington, 30University of Washington, 31University of Washington, 32University of Washington, 33University of Washington

If the ethnic makeup of the astronomy profession is to achieve parity with the general population within one generation (~30 years), the number of underrepresented minorities earning graduate degrees in astronomy and astrophysics must increase in the coming decade by a factor of 5 to 10. To accomplish this, the profession must develop and invest in mechanisms to more effectively move individuals across critical educational junctures to the PhD and beyond. Early and continuous research engagement starting in the undergraduate years is critical to this vision, in which the federally funded research internship programs (e. Read More

2009Mar
Affiliations: 1NOAO, 2AAS, 3Columbia University, 4Columbia University, 5University of Washington, 6Rutgers University, 7Caltech, 8Caltech, 9Vanderbilt University, Pres. of the Nat. Soc. of Hispanic Physicists, 10Rutgers University, 11University of Maryland, College Park, 12Washington State University, 13NOAO, 14Western Kentucky University, 15University of Notre Dame, 16Spitzer Science Center, 17STScI, 18Princeton University, 19South Carolina State University, 20MIT, 21Faculty Project Leader, 22University of Washington, 23University of Washington, 24University of Washington, 25University of Washington, 26University of Washington, 27University of Washington, 28University of Washington, 29University of Washington, 30University of Washington, 31University of Washington, 32University of Washington, 33University of Washington

In order to attract, recruit and retain underrepresented minority students to pursue Astronomy and related fields, we must ensure that there continues to be a well qualified pool of graduate and undergraduate students from which to recruit. This required pool of people are today's elementary, middle and high school students. The Astronomy community must be proactive in demonstrating the importance of pursing scientific study and careers to these students and their parents. Read More

The ROSAT All-Sky Survey (RASS) was the first imaging X-ray survey of the entire sky. While X-ray source counterparts are known to range from distant quasars to nearby M dwarfs, the RASS data alone are often insufficient to determine the nature of an X-ray source. As a result, large-scale follow-up programs are required to construct samples of known X-ray emitters. Read More

We report the detection of a radial velocity companion to the extremely low mass white dwarf LP400-22. The radial velocity of the white dwarf shows variations with a semi-amplitude of 119 km/s and a 0.98776 day period, which implies a companion mass of M > 0. Read More

2009Mar
Affiliations: 1Columbia U., 2Columbia U., 3U. of Washington, 4Gemini Obs., 5U. of Washington, 6U. of Arizona & Steward Obs.

We have conducted a search for pulsar companions to 15 low-mass white dwarfs (LMWDs; M < 0.4 M_Sun) at 820 MHz with the NRAO Green Bank Telescope (GBT). These LMWDs were spectroscopically identified in the Sloan Digital Sky Survey (SDSS), and do not show the photometric excess or spectroscopic signature associated with a companion in their discovery data. Read More

We present 348 X-ray emitting stars identified from correlating the Extended Chandra Multiwavelength Project (ChaMP), a serendipitous wide-area X-ray survey, with the Sloan Digital Sky Survey (SDSS). We use morphological star/galaxy separation, an SDSS quasar catalog, an optical color-magnitude cut, and X-ray data quality tests to create our catalog, the ChaMP Extended Stellar Survey (ChESS), from a sample of 2121 matched ChaMP/SDSS sources. Our cuts retain 92% of the spectroscopically confirmed stars while excluding 99. Read More

We study galaxies that host both nuclear star clusters and active galactic nuclei (AGN) implying the presence of a massive black hole. We select a sample of 176 galaxies with previously detected nuclear star clusters that range from ellipticals to late-type spirals. We search for AGN in this sample using optical spectroscopy and archival radio and X-ray data. Read More

2007Jul
Affiliations: 1Harvard Smithsonian Center for Astrophysics, 2University of Washington, 3Lawrence Berkeley National Laboratory, 4Harvard Smithsonian Center for Astrophysics, 5Lawrence Berkeley National Laboratory, 6Princeton University Observatory, 7Columbia University, 8University of Washington, 9University of Washington, 10Univeristy of California Berkeley, 11Harvard Smithsonian Center for Astrophysics, 12University of Washington, 13University of Washington, 14University of Washington, 15University of Washington, 16University of Washington, 17Penn State, 18University of Washington
Category: Astrophysics

The Sloan Digital Sky Survey (SDSS) and Two Micron All Sky Survey (2MASS) are rich resources for studying stellar astrophysics and the structure and formation history of the Galaxy. As new surveys and instruments adopt similar filter sets, it is increasingly important to understand the properties of the ugrizJHKs stellar locus, both to inform studies of `normal' main sequence stars as well as for robust searches for point sources with unusual colors. Using a sample of ~600,000 point sources detected by SDSS and 2MASS, we tabulate the position and width of the ugrizJHKs stellar locus as a function of g-i color, and provide accurate polynomial fits. Read More

We describe further results of a program aimed to yield ~10^4 fully characterized optical identifications of ROSAT X-ray sources. Our program employs X-ray data from the ROSAT All-Sky Survey (RASS), and both optical imaging and spectroscopic data from the Sloan Digital Sky Survey (SDSS). RASS/SDSS data from 5740 deg^2 of sky spectroscopically covered in SDSS Data Release 5 (DR5) provide an expanded catalog of 7000 confirmed quasars and other AGN that are probable RASS identifications. Read More

We discuss the panchromatic properties of 99,088 galaxies selected from the SDSS Data Release 1 spectroscopic sample (a flux-limited sample for 1360 deg^2). These galaxies are positionally matched to sources detected by ROSAT, GALEX, 2MASS, IRAS, GB6, FIRST, NVSS and WENSS. We find strong correlations between the detection fraction at other wavelengths and optical properties such as flux, colors, and emission-line strengths. Read More

Only seven radio-quiet isolated neutron stars (INSs) emitting thermal X rays are known, a sample that has yet to definitively address such fundamental issues as the equation of state of degenerate neutron matter. We describe a selection algorithm based on a cross-correlation of the ROSAT All-Sky Survey (RASS) and the Sloan Digital Sky Survey (SDSS) that identifies X-ray error circles devoid of plausible optical counterparts to the SDSS g~22 magnitudes limit. We quantitatively characterize these error circles as optically blank; they may host INSs or other similarly exotic X-ray sources such as radio-quiet BL Lacs, obscured AGN, etc. Read More

2005May
Affiliations: 1Univ. of Washington, 2Univ. of Washington, 3Univ. of Washington, 4Kapteyn Institute, 5Cornell Univ, 6Univ. of Washington, 7Univ. of Washington, 8Univ. of Pittsburgh, 9Princeton Univ, 10Princeton Univ, 11Princeton Univ, 12Princeton Univ, 13Univ. of Washington, 14Univ. of Washington, 15Univ. of Washington, 16Univ. of Washington, 17Univ. of Washington, 18Univ. of Washington, 19Univ. of Washington, 20Univ. of Washington, 21Univ. of Washington
Category: Astrophysics

We discuss the UV, optical, and IR properties of the SDSS sources detected by GALEX as part of its All-sky Imaging Survey Early Release Observations. Virtually all of the GALEX sources in the overlap region are detected by SDSS. GALEX sources represent ~2. Read More

This paper continues the series that identifies new cataclysmic variables found in the Sloan Digital Sky Survey. We present 36 cataclysmic variables and one possible symbiotic star from Sloan spectra obtained during 2002, of which 34 are new discoveries, 2 are known dwarf novae (BC UMa, KS UMa) and one is a known CV identified from the 2dF survey. The positions, colors and spectra of all 37 systems are presented, along with follow-up spectroscopic/photometric observations of 10 systems. Read More

Many open questions in X-ray astronomy are limited by the relatively small number of objects in uniform optically-identified samples, especially when rare subclasses are considered, or subsets isolated to search for evolution or correlations between wavebands. We describe initial results of a program aimed to ultimately yield 10^4 X-ray source identifications--a sample about an order of magnitude larger than earlier efforts. The technique employs X-ray data from the ROSAT All-Sky Survey (RASS), and optical imaging and spectroscopic followup from the Sloan Digital Sky Survey (SDSS). Read More

2003Apr
Affiliations: 1Columbia Astrophysics Laboratory, Columbia University, 2Department of Astronomy, University of Washington, 3Columbia Astrophysics Laboratory, Columbia University
Category: Astrophysics

We have observed the Galactic supernova remnant G16.7+0.1 for 13 ks using the EPIC cameras aboard the XMM-Newton X-ray Observatory, producing the first X-ray image of the remnant. Read More

2001Oct
Affiliations: 1Univ. of Washington, 2Columbia Univ, 3Columbia Univ
Category: Astrophysics

We have observed the Galactic supernova remnant G16.7+0.1 for 13 ks using the EPIC cameras aboard the XMM-Newton X-ray Observatory, producing the first detection of the SNR outside of the radio band. Read More

The commissioning year of the Sloan Digital Sky Survey has demonstrated that many cataclysmic variables have been missed in previous surveys with brighter limits. We report the identification of 22 cataclysmic variables, of which 19 are new discoveries and 3 are known systems (SW UMa, BH Lyn and Vir4). A compendium of positions, colors and characteristics of these systems obtained from the SDSS photometry and spectroscopy is presented along with data obtained during follow-up studies with the Apache Point Observatory (APO) and Manastash Ridge Observatory (MRO) telescopes. Read More