T. L. Aldcroft

The Astronomical Observatory of Brera, Merate, Lombardy, Italy

Are you T. L. Aldcroft?

Claim your profile

Publications (110)229.29 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The Cygnus OB2 association is the largest concentration of young and massive stars within 2 kpc of the Sun, including an estimated 65 O-type stars and hundreds of OB stars. The Chandra Cygnus OB2 Legacy Survey is a large imaging program undertaken with the Advanced CCD Imaging Spectrometer onboard the Chandra X-ray Observatory. The survey has imaged the central 0.5 deg^2 of the Cyg OB2 association with an effective exposure of 120ks and an outer 0.35 deg^2 area with an exposure of 60ks. Here we describe the survey design and observations, the data reduction and source detection, and present a catalog of 8,000 X-ray point sources. The survey design employs a grid of 36 heavily (~50%) overlapping pointings, a method that overcomes Chandra's low off-axis sensitivity and produces a highly uniform exposure over the inner 0.5 deg^2. The full X-ray catalog is described here and is made available online.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present the first public version (v0.2) of the open-source and community-developed Python package, Astropy. This package provides core astronomy-related functionality to the community, including support for domain-specific file formats such as Flexible Image Transport System (FITS) files, Virtual Observatory (VO) tables, and common ASCII table formats, unit and physical quantity conversions, physical constants specific to astronomy, celestial coordinate and time transformations, world coordinate system (WCS) support, generalized containers for representing gridded as well as tabular data, and a framework for cosmological transformations and conversions. Significant functionality is under active development, such as a model fitting framework, VO client and server tools, and aperture and point spread function (PSF) photometry tools. The core development team is actively making additions and enhancements to the current code base, and we encourage anyone interested to participate in the development of future Astropy versions.
  • [Show abstract] [Hide abstract]
    ABSTRACT: The formation of stars in massive clusters is one of the main modes of the star formation process. However, the study of massive star forming regions is hampered by their typically large distances to the Sun. One exception to this is the massive star forming region Cygnus OB2 in the Cygnus X region, at the distance of about 1400 pc. Cygnus OB2 hosts very rich populations of massive and low-mass stars, being the best target in our Galaxy to study the formation of stars, circumstellar disks, and planets in presence of massive stars. In this paper we combine a wide and deep set of photometric data, from the r band to 24 micron, in order to select the disk bearing population of stars in Cygnus OB2 and identify the class I, class II, and stars with transition and pre-transition disks. We selected 1843 sources with infrared excesses in an area of 1 degree x 1 degree centered on Cyg OB2 in several evolutionary stages: 8.4% class I, 13.1% flat-spectrum sources, 72.9% class II, 2.3% pre-transition disks, and 3.3% transition disks. The spatial distribution of these sources shows a central cluster surrounded by a annular overdensity and some clumps of recent star formation in the outer region. Several candidate subclusters are identified, both along the overdensity and in the rest of the association.
    The Astrophysical Journal 06/2013; 773(2). DOI:10.1088/0004-637X/773/2/135 · 6.28 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Striking similarities have been seen between accretion signatures of Galactic X-ray binary (XRB) systems and active galactic nuclei (AGN). XRB spectral states show a V-shaped correlation between X-ray spectral hardness and Eddington ratio as they vary, and some AGN samples reveal a similar trend, implying analogous processes at vastly larger masses and timescales. To further investigate the analogies, we have matched 617 sources from the Chandra Source Catalog to SDSS spectroscopy, and uniformly measured both X-ray and optical spectral characteristics across a broad range of AGN and galaxy types. We provide useful tabulations of X-ray spectral slope for broad and narrow line AGN, star-forming and passive galaxies and composite systems, also updating relationships between optical (Ha and [OIII]) line emission and X-ray luminosity. We further fit broadband spectral energy distributions with a variety of templates to estimate bolometric luminosity. Our results confirm a significant trend in AGN between X-ray spectral hardness and Eddington ratio expressed in X-ray luminosity, albeit with significant dispersion. The trend is not significant when expressed in the full bolometric or template-estimated AGN luminosity. We also confirm a relationship between the X-ray/optical spectral slope aox, and Eddington ratio, but it may not follow the trend predicted by analogy with XRB accretion states.
    The Astrophysical Journal 06/2013; DOI:10.1088/0004-637X/778/2/188 · 6.28 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The young massive cluster Cyg OB2 is the closest massive star forming region to the Sun, with hundreds of OB members, and then the best target in the Milky Way to study the feedback of massive stars on the star formation process. To study in detail the stellar population of such a unique target, Cyg OB2 has been observed with GTC/OSIRIS and Chandra/ACIS-I. We present the OSIRIS observations, the catalog and the preliminary scientific results.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present the X-ray spectral analysis of the 390 brightest extragalactic sources in the Chandra-COSMOS catalog, showing at least 70 net counts in the 0.5-7 keV band. This sample has a 100% completeness in optical-IR identification, with 75% of the sample having a spectroscopic redshift and 25% a photometric redshift. Our analysis allows us to accurately determine the intrinsic absorption, the broad band continuum shape ({\Gamma}) and intrinsic L(2-10) distributions, with an accuracy better than 30% on the spectral parameters for 95% of the sample. The sample is equally divided in type-1 (49.7%) and type-2 AGN (48.7%) plus few passive galaxies at low z. We found a significant difference in the distribution of {\Gamma} of type-1 and type-2, with small intrinsic dispersion, a weak correlation of {\Gamma} with L(2-10) and a large population (15% of the sample) of high luminosity, highly obscured (QSO2) sources. The distribution of the X ray/Optical flux ratio (Log(FX /Fi)) for type-1 is narrow (0 < X/O < 1), while type-2 are spread up to X/O = 2. The X/O correlates well with the amount of X-ray obscuration. Finally, a small sample of Compton thick candidates and peculiar sources is presented. In the appendix we discuss the comparison between Chandra and XMM-Newton spectra for 280 sources in common. We found a small systematic difference, with XMM-Newton spectra that tend to have softer power-laws and lower obscuration.
    Monthly Notices of the Royal Astronomical Society 02/2013; 431(1). DOI:10.1093/mnras/stt222 · 5.23 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Studies of quasar mass outflows are rapidly reshaping our understanding of physics near the supermassive black hole (SMBH). The ~parsec scale emitting/absorbing regions near SMBHs will remain spatially unresolved for the foreseeable future (milliarcsec at z ~ 0.01). Spectroscopic variability timescale information can, however, constrain the structure, stability, location, and dynamics of the emitting and absorbing gas near the SMBH. Though outflows likely accompany all luminous accretion disks, broad absorption line (BAL) quasars provide the most dramatic examples — their massive outflows display P-Cygni profiles that span velocities to ~0.3c. We present multi-epoch spectroscopy of seventeen BAL QSOs using the Fred Lawrence Whipple Observatory's 1.5m telescope's FAST Spectrograph. These objects were identified as BALs in SDSS, observed with Chandra, and then monitored with FAST at observed-frame cadences of 1, 3, 9, 27, and 81 days, as well as 1 and 2 years. We also monitor a set of non-BAL quasars with matched redshift and luminosity as controls. We identify significant variability in the BALs, particularly at the 1 and 2 year cadences, and use its magnitude and frequency to constrain the outflows impacting the broad absorption line region.
    American Astronomical Society, AAS Meeting #221, Long Beach, CA; 01/2013
  • [Show abstract] [Hide abstract]
    ABSTRACT: The equatorial 2 deg2 COSMOS area is the only large field for which a complete, deep, pan-chromatic data set exists, from an outstanding survey effort, and that all large telescopes can observe. Now, this pioneering and ambitious COSMOS survey is undergoing major extension, pushing its frontiers via the newly approved Chandra COSMOS Legacy Survey, the second largest Chandra proposal ever approved.'COSMOS-Legacy' will uniformly cover the 1.7 deg2 COSMOS/HST field with 2.8 Ms of Chandra ACIS-I imaging at ~160 ksec depth. This project expands the current deep C-COSMOS area by a factor of ~3 at ~3e-16 (1.45 vs 0.44 deg2). This will be achieved with 56x50 ks tiles covering a total area of 2.2 deg2, which will be observed during Chandra Cycle 14. The area and depth of COSMOS Legacy are designed to detect ~{40 zgt4, and ~}4 zgt5 Large Scale Structures on gt15 arcmin scales. These structures have proven to connect luminous AGN (over 200 at zgt3 will be detected) and sub-mm galaxies. COSMOS Legacy will also probe mini-quasars at zgt7, using anistotropies of the unresolved X-ray Background, and the masses of the Dark Matter halos hosting X-ray AGN up to 3, via autocorrelation functions on ~30arcmin scales. To fully achieve these goals, COSMOS Legacy is complemented by spectroscopic follow-up with DEIMOS and MOSFIRE at Keck and KMOS at the VLT and FMOS at Subaru, just approved observations with Spitzer and JVLA, and with harder (5-80 keV) X-ray imaging with NuSTAR. In the near future, observations with Subaru HyperSuprimeCam (grizY) to r(AB)=28.2 are planned.
    American Astronomical Society Meeting Abstracts; 01/2013
  • [Show abstract] [Hide abstract]
    ABSTRACT: Optical catalog in riz bands in a 30'x30' area around CygnusOB2. (1 data file).
  • [Show abstract] [Hide abstract]
    ABSTRACT: The coalescence of two SMBHs in galaxy major merger gives rise to the strongest Gravitational Wave (GW) events in the universe. Typically, the GW emission is asymmetric and causes the newly merged single SMBH to displace from the galaxy center of few parsecs. Under particular condition of BH spin and mass ratio, the SMBH can gain a significant velocity (up to ~5000km/s) and it may be displaced by several kpc. If the SMBH is ejected from the galaxy, or even if wanders through the halo for several Gyrs, it will continue to shine for 10^6-10^7 yr, until it exhausts the fuel and is no longer recognizable as an active SMBH. The partial or total absence of the SMBH from the galaxy center has strong implications on the SF history of the galaxy. Despite predicted by theoretical models of structure formation, GW recoiling SMBHs are very hard to detect. The recoils with high probability have a very small velocity resulting in undetectable offsets, those with low probability can escape easily from the galaxy and not been recognized as such. We discovered in the COSMOS survey CID-42 (z=0.359), the best candidate recoiling SMBH to date, just caught when still active. CID-42 clearly shows both the presence of two compact sources, ~2.5 kpc embedded in the same galaxy in HST imaging, and a ~1100km/s velocity offset between the narrow and broad components of Hα, in 3 optical spectra. High resolution Chandra data were crucial to resolve the X-ray emission from the two optical sources and determines the AGN activity level of each. The results clearly favor the recoiling scenario for this source. Models & simulations have been developed to explain the observed properties of CID-42.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In order to fully understand the gravitational collapse of molecular clouds, the star formation process and the evolution of circumstellar disks, these phenomena must be studied in different Galactic environments with a range of stellar contents and positions in the Galaxy. The young massive association Cygnus OB2, in the Cygnus-X region, is an unique target to study how star formation and the evolution of circumstellar disks proceed in the presence of a large number of massive stars. We present a catalog obtained with recent optical observations in r,i,z filters with OSIRIS, mounted on the $10.4\,m$ GTC telescope, which is the deepest optical catalog of Cyg OB2 to date. The catalog consist of 64157 sources down to M=0.15 solar masses at the adopted distance and age of Cyg OB2. A total of 38300 sources have good photometry in all three bands. We combined the optical catalog with existing X-ray data of this region, in order to define the cluster locus in the optical diagrams. The cluster locus in the r-i vs. i-z diagram is compatible with an extinction of the optically selected cluster members in the 2.64<AV<5.57 range. We derive an extinction map of the region, finding a median value of AV=4.33 in the center of the association, decreasing toward the north-west. In the color-magnitude diagrams, the shape of the distribution of main sequence stars is compatible with the presence of an obscuring cloud in the foreground at about 850+/-25 pc from the Sun.
    The Astrophysical Journal Supplement Series 08/2012; 202(2). DOI:10.1088/0067-0049/202/2/19 · 14.14 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present Chandra High Resolution Camera observations of CID-42, a candidate recoiling supermassive black hole (SMBH) at z = 0.359 in the COSMOS survey. CID-42 shows two optical compact sources resolved in the HST/ACS image embedded in the same galaxy structure and a velocity offset of ~1300 km s–1 between the Hβ broad and narrow emission line, as presented by Civano et al. Two scenarios have been proposed to explain the properties of CID-42: a gravitational wave (GW) recoiling SMBH and a double Type 1/Type 2 active galactic nucleus (AGN) system, where one of the two is recoiling because of slingshot effect. In both scenarios, one of the optical nuclei hosts an unobscured AGN, while the other one, either an obscured AGN or a star-forming compact region. The X-ray Chandra data allow us to unambiguously resolve the X-ray emission and unveil the nature of the two optical sources in CID-42. We find that only one of the optical nuclei is responsible for the whole X-ray unobscured emission observed and a 3σ upper limit on the flux of the second optical nucleus is measured. The upper limit on the X-ray luminosity plus the analysis of the multiwavelength spectral energy distribution indicate the presence of a star-forming region in the second source rather than an obscured SMBH, thus favoring the GW recoil scenario. However, the presence of a very obscured SMBH cannot be fully ruled out. A new X-ray feature, in a SW direction with respect to the main source, is discovered and discussed.
    The Astrophysical Journal 05/2012; 752(1):49. DOI:10.1088/0004-637X/752/1/49 · 6.28 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The Chandra COSMOS Survey (C-COSMOS) is a large, 1.8 Ms, Chandra program that has imaged the central 0.9 deg^2 of the COSMOS field down to limiting depths of 1.9 10^-16 erg cm^-2 s-1 in the 0.5-2 keV band, 7.3 10^-16 erg cm^-2 s^-1 in the 2-10 keV band, and 5.7 10^-16 erg cm^-2 s-1 in the 0.5-10 keV band. In this paper we report the i, K and 3.6micron identifications of the 1761 X-ray point sources. We use the likelihood ratio technique to derive the association of optical/infrared counterparts for 97% of the X-ray sources. For most of the remaining 3%, the presence of multiple counterparts or the faintness of the possible counterpart prevented a unique association. For only 10 X-ray sources we were not able to associate a counterpart, mostly due to the presence of a very bright field source close by. Only 2 sources are truly empty fields. Making use of the large number of X-ray sources, we update the "classic locus" of AGN and define a new locus containing 90% of the AGN in the survey with full band luminosity >10^42 erg/s. We present the linear fit between the total i band magnitude and the X-ray flux in the soft and hard band, drawn over 2 orders of magnitude in X-ray flux, obtained using the combined C-COSMOS and XMM-COSMOS samples. We focus on the X-ray to optical flux ratio (X/O) and we test its known correlation with redshift and luminosity, and a recently introduced anti-correlation with the concentration index (C). We find a strong anti-correlation (though the dispersion is of the order of 0.5 dex) between C and X/O, computed in the hard band, and that 90% of the obscured AGN in the sample with morphological information live in galaxies with regular morphology (bulgy and disky/spiral), suggesting that secular processes govern a significant fraction of the BH growth at X-ray luminosities of 10^43- 10^44.5 erg/s.
    The Astrophysical Journal Supplement Series 05/2012; 201(2). DOI:10.1088/0067-0049/201/2/30 · 14.14 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present Chandra High Resolution Camera observations of CID-42, a candidate recoiling supermassive black hole (SMBH) at z=0.359 in the COSMOS survey. CID-42 shows two optical compact sources resolved in the HST/ACS image embedded in the same galaxy structure and a velocity offset of ~1300 km/s between the H\beta\ broad and narrow emission line, as presented by Civano et al. (2010). Two scenarios have been proposed to explain the properties of CID-42: a GW recoiling SMBH and a double Type 1/ Type 2 AGN system, where one of the two is recoiling because of slingshot effect. In both scenario, one of the optical nuclei hosts an unobscured AGN, while the other one, either an obscured AGN or a star forming compact region. The X-ray Chandra data allow to unambiguously resolve the X-ray emission, and unveil the nature, of the two optical sources in CID-42. We find that only one of the optical nuclei is responsible for the whole X-ray unobscured emission observed and a 3sigma upper limit on the flux of the second optical nucleus is measured. The upper limit on the X-ray luminosity plus the analysis of the multiwavelength spectral energy distribution indicate the presence of a starforming region in the second source rather than an obscured SMBH, thus favoring the GW recoil scenario. However the presence of a very obscured SMBH cannot be fully ruled-out. A new X-ray feature, in a SW direction with respect to the main source, is discovered and discussed.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: From optical spectroscopy of X-ray sources observed as part of ChaMP, we present redshifts and classifications for a total of 1569 Chandra sources from our targeted spectroscopic follow up using the FLWO, SAAO, WIYN, CTIO, KPNO, Magellan, MMT and Gemini telescopes, and from archival SDSS spectroscopy. We classify the optical counterparts as 50% BLAGN, 16% NELG, 14% ALG, and 20% stars. We detect QSOs out to z~5.5 and galaxies out to z~3. We have compiled extensive photometry from X-ray to radio bands. Together with our spectroscopic information, this enables us to derive detailed SEDs for our extragalactic sources. We fit a variety of templates to determine bolometric luminosities, and to constrain AGN and starburst components where both are present. While ~58% of X-ray Seyferts require a starburst event to fit observed photometry only 26% of the X-ray QSO population appear to have some kind of star formation contribution. This is significantly lower than for the Seyferts, especially if we take into account torus contamination at z>1 where the majority of our X-ray QSOs lie. In addition, we observe a rapid drop of the percentage of starburst contribution as X-ray luminosity increases. This is consistent with the quenching of star formation by powerful QSOs, as predicted by the merger model, or with a time lag between the peak of star formation and QSO activity. We have tested the hypothesis that there should be a strong connection between X-ray obscuration and star-formation but we do not find any association between X-ray column density and star formation rate both in the general population or the star-forming X-ray Seyferts. Our large compilation also allows us to report here the identification of 81 XBONG, 78 z>3 X-ray sources and 8 Type-2 QSO candidates. Also we have identified the highest redshift (z=5.4135) X-ray selected QSO with optical spectroscopy.
    The Astrophysical Journal Supplement Series 04/2012; 200(2). DOI:10.1088/0067-0049/200/2/17 · 14.14 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Broad absorption line (BAL) quasars probe the high velocity gas ejected by luminous accreting black holes. BAL variability timescales place constraints on the size, location, and dynamics of the emitting and absorbing gas near the supermassive black hole. We present multi-epoch spectroscopy of seventeen BAL QSOs from the Sloan Digital Sky Survey (SDSS) using the Fred Lawrence Whipple Observatory's 1.5m telescope's FAST Spectrograph. These objects were identified as BALs in SDSS, observed with Chandra, and then monitored with FAST at observed-frame cadences of 1, 3, 9, 27, and 81 days, as well as 1 and 2 years. We also monitor a set of non-BAL quasars with matched redshift and luminosity as controls. We identify significant variability in the BALs, particularly at the 1 and 2 year cadences, and use its magnitude and frequency to constrain the outflows impacting the broad absorption line region.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Kinetic energy carried by AGN winds and jets may rival radiation as the dominant feedback mechanism regulating galaxy-SMBH co-evolution. Though outflows likely accompany all luminous accretion disks, broad absorption line quasars (BALQSOs) provide the most dramatic astrophysical examples; their massive outflows display P-Cygni profiles that span velocities up to 0.3c and are visible in the spectra of 15-40% of optically-selected quasars. Spectroscopic variability studies of BALQSOs probe the structure, stability, location, and dynamics of the emitting and absorbing gas near the SMBH and can provide insight into connections between AGN feedback and host galaxy formation and evolution. We report on a multi-year spectroscopic campaign that monitors seventeen BALQSOs (identified originally in the SDSS) using the Fred Lawrence Whipple Observatory's 1.5m telescope's FAST spectrograph. These targets have Chandra X-ray data and have been repeatedly observed with FAST, in regular cadences from one day to two years -- a 6 year cadence is planned for spring 2012. We identify variability in the broad absorption line region, assess its significance, magnitude, and frequency and discuss the constraints these investigations can place on QSO outflows.
    American Astronomical Society, AAS Meeting #219, Austin, TX; 01/2012
  • [Show abstract] [Hide abstract]
    ABSTRACT: Black hole and galaxy co-evolution models predict a phase in which multiple galaxies with active black holes interact, with visible signatures of interaction, and that their activity may be stimulated by tidal disruptions of their ISM. Several studies have been recently conducted to prove the existence of this phase. However, a proper multiwavelength characterization of galaxy pairs is still missing. We present analysis of X-ray emitting galaxy pairs selected in the Chandra COSMOS survey. The sources in each pair are within a redshift difference of 0.2 and a projected separation of 10 arcseconds, corresponding to projected physical separations ranging from 27 kpc to 82 kpc. In order to characterize the pairs in the context of the black hole/galaxy co-evolution scenario, we i) fit spectral energy distributions to determine the relative AGN and galaxy contributions, ii) calculated X-ray luminosities and hardness ratios to check the active nature of the black holes and to get a sense of the obscuration levels, iii) examined the morphologies for signatures of mergers, and iv) determined relative velocities from available spectra. Active black holes are present in all of the galaxies, as they are very luminous in the X-ray band, though mildly obscured. In most of the sources, the host galaxy out shines the nuclear light in the optical band. In several lower redshift pairs, where morphological features are more easily observed, we see disturbed morphology and tidal structures, signatures of a first close passage. This work is supported in part by the NSF REU and DOD ASSURE programs under NSF grant no. 0754568 and by the Smithsonian Institution.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Broad absorption line (BAL) quasars probe the high-velocity gas ejected by luminous accreting black holes. BAL variability timescales place constraints on the size, location, and dynamics of the emitting and absorbing gas near the supermassive black hole. We present multi-epoch spectroscopy of seventeen BAL QSOs from the Sloan Digital Sky Survey (SDSS) using the Fred Lawrence Whipple Observatory's 1.5m telescope's FAST Spectrograph. These objects were identified as BALs in SDSS, observed with Chandra, and then monitored with FAST at observed-frame cadences of 1, 3, 9, 27, and 81 days, as well as 1 and 2 years. We also monitor a set of non-BAL quasars with matched redshift and luminosity as controls. We identify significant variability in the BALs, particularly at the 1 and 2 year cadences, and use its magnitude and frequency to constrain the outflows impacting the broad absorption line region.
    AGN Winds in Charleston, ASP Conference Series, Chareston, SC; 10/2011
  • [Show abstract] [Hide abstract]
    ABSTRACT: From optical spectroscopy of X-ray sources observed as part of the Chandra Multiwavelength Project (ChaMP), we present redshifts and classifications for a total of 1569 Chandra sources from our targeted spectroscopic follow-ups using the FLWO 1.5m, WIYN 3.5m, CTIO 4m, Magellan 6.5m, MMT 6.5m and Gemini 8m telescopes, and from archival SDSS spectroscopy. We classify the optical counterparts as 50% broad line AGN, 16% emission line galaxies, 14%s absorption line galaxies, and 20% stars. We detect QSOs out to z 5.5 and galaxies out to z 3. We have compiled extensive photometry, including X-ray (ChaMP), UV (GALEX), Optical (SDSS), NIR (UKIDSS, 2MASS), MIR (WISE) and Radio (FIRST, NVSS) bands. Together with our spectroscopic information, this enables us to derive detailed spectral energy distributions (SEDs) for all our extragalactic sources. We fit a variety of template SEDs to determine bolometric luminosities, and to constrain AGN and starburst components where both present. The latter in combination to the derived X-ray spectral fits for all our sources will provide us with a large sample to be able to study in detail the AGN/Star-formation coevolution and the relationship between nuclear obscuration and star-formation.

Publication Stats

962 Citations
229.29 Total Impact Points

Institutions

  • 2012
    • The Astronomical Observatory of Brera
      Merate, Lombardy, Italy
  • 2000–2012
    • Harvard-Smithsonian Center for Astrophysics
      • Smithsonian Astrophysical Observatory
      Cambridge, Massachusetts, United States
  • 2010
    • University of Washington Seattle
      • Department of Astronomy
      Seattle, Washington, United States
  • 1994
    • The University of Arizona
      • Large Binocular Telescope Observatory
      Tucson, Arizona, United States
  • 1992
    • Stanford Medicine
      Stanford, California, United States