Jane Gregorio-Hetem

The Gemini NICI Planet-Finding Campaign : Discovery of a Substellar L Dwarf Companion to the Nearby Young M Dwarf CD-35 2722

We present the discovery of a wide (67 AU) substellar companion to the nearby (21 pc) young solar-metallicity M1 dwarf CD-35 2722, a member of the ~100 Myr AB Doradus association. Two epochs of astrometry from the NICI Planet-Finding Campaign confirm that CD-35 2722 B is physically associated with the primary star. Near-IR spectra indicate a spectral type of L4\pm1 with a moderately low surface gravity, making it one of the coolest young companions found to date. The absorption lines and near-IR continuum shape of CD-35 2722 B agree especially well the dusty field L4.5 dwarf 2MASS J22244381-0158521, while the near-IR colors and absolute magnitudes match those of the 5 Myr old L4 planetary-mass companion, 1RXS J160929.1-210524 b. Overall, CD-35 2722 B appears to be an intermediate-age benchmark for L-dwarfs, with a less peaked H-band continuum than the youngest objects and near-IR absorption lines comparable to field objects. We fit Ames-Dusty model atmospheres to the near-IR spectra and find T=1700-1900 K and log(g) =4.5\pm0.5. The spectra also show that the radial velocities of components A and B agree to within \pm10 km/s, further confirming their physical association. Using the age and bolometric luminosity of CD-35 2722 B, we derive a mass of 31\pm8 Mjup from the Lyon/Dusty evolutionary models. Altogether, young late-M to mid-L type companions appear to be over-luminous for their near-IR spectral type compared to field objects, in contrast to the under-luminosity of young late-L and early-T dwarfs.

Open issues in local star formation

Stellar Groups and Associations.- Major Unsolved Problems in Star Formation.- The Stellar Mass Function of Galactic Clusters and Its Evolution.- Encounters and Close Fly-Bys of Galactic Clusters and Associations in the Past 50 Myr.- Solar-Type Post-T Tauri Stars in the Nearest OB Subgroups.- NGC 2362: The Shape of the Pre-Main-Sequence from A-Stars to Brown Dwarfs.- Young Stars and Their Circumstellar Disks in the ? Orionis Cluster.- The Oph-Sco-Lup-Cen-Cru-Mus-Cha Star-formation Region.- The Gas-to-Dust Ratio and Metallurgy of Nearby Dark Clouds Probed by X-ray Absorption Measurements.- Sacy - A Search for Associations Containing Young Stars.- Age Determination of the Ursa Major Association.- Young Stellar Objects.- Accretion Powered Emission in Young Stellar Objects.- The Pre-Main Sequence Spectroscopic Binary AK Sco.- Survey of Young Stellar Objects Associated with Molecular Clouds.- The Stellar Population of Embedded Galactic Massive Star Clusters.- Spectroscopic Analysis of 131 Herbig Ae/Be Candidate Stars.- Classification of the Pico Dos Dias Survey Herbig Ae/Be Stars.- Chemical Composition Study of an Accretion Episode in the Herbig Candidate Star PDS080.- Magnetically Channeled Accretion in T Tauri Stars.- Properties of Young Stellar Objects from High Resolution Near Infrared Spectroscopy.- Probing the Circumstellar Structure of Pre-main Sequence Stars.- Accretion Signatures in the X-Ray Spectrum of TW Hya.- Post-T Tauri Stars Rotation in Associations.- Star Formation in Canis Majoris.- X-ray Emission from NGC 2362.- Accretion and Ejection.- The Origin of Jets in Young Stars.- Non Coeval Young Multiple Systems?.- Brown Dwarfs.- Brown Dwarfs in Young Open Clusters.- Brown Dwarf Companions.- Observational Clues to Brown Dwarf Origins.- Surface Gravity & Mass in Young Brown Dwarfs and Planemos.- Disks, Outflows and Jets.- Fu Orionis Eruptions and the Formation of Close Binaries.- Seds of Flared Dust Disks.- On the Alignment of T Tauri Stars with the Local Magnetic Field.- Temporal Evolution of Main Sequence Dusty Disks.- Numerical Simulations of Young Stellar Jets: From One Tenth to Parsec Scales.- Alfven Waves in Disks, Outflows and Jets.- Early Stages of Star Formation.- Submillimeter Studies of Protostellar Cores.- Detection of a Collimated Jet Towards the High-Mass Protostar IRAS 16547-4247.- Disks and Halos in Pre-Main-Sequence Stars.- Radiative Transfer in Prestellar Cores: A Monte Carlo Approach.- The ISM Conditions for Star Formation.- The Initial Conditions for Star Formation.- Chemical Signatures of New Star Formation Toward Young Stellar Clusters.- Collapse of Molecular Clouds Leading to Star Formation.- Star Formation in Globules.- Simba Survey Toward High-Mass Star Forming Regions in the Southern Hemisphere.- Conference Summary and Conclusions.

Discovery of a Luminous Quasar in the Nearby Universe

In the course of the Pico dos Dias survey (PDS), we identified the stellar-like object PDS 456 at coordinates a 5 17 h 28 m 19 s d 52 147159550 (epoch 2000), with a relatively nearby (z 5 0.184) and bright (B 5 14.69) quasar. Its position at Galactic coordinates l 5 107 b 51 117 .2, near the bulge of the Galaxy, may explain why it was not detected before. The optical spectrum of PDS 456 is typical of a luminous quasar, showing a broad (FWHM » 4000 km s 21 )H bline, very intense Fe ii lines, and a weak [O iii] l5007 line. PDS 456 is associated to the infrared source IRAS 1725421413 with a 60 mm infrared luminosity L60 5 3.8 # 10 45 ergs s 21 . The relatively flat slopes in the infrared [ a(25, 60) 52 0.33 and a(12, 25) 52 0.78] and a flat power index in the optical (Fn / n 20.72 ) may indicate a low dust content. A good match between the position of PDS 456 and the position of the X-ray source RXS J172819.32141600 implies an X-ray luminosity LX 5 2.8 # 10 44 ergs s 21 . The good correlation between the strength of the emission lines in the optical and the X-ray luminosity, as well as the steep optical to X-ray index estimated (aOX 52 1.64), suggests that PDS 456 is radio quiet. A radio survey previously performed in this region yields an upper limit for radio power at about 5 GHz of approximately 2.6 # 10 30 ergs 21 Hz 21 . We estimate the Galactic reddening in this line of sight to be AB . 2.0, implying an absolute magnitude MB 52 26.7 (using H0 5 75 km s 21 Mpc 21 and q0 5 0). In the optical, PDS 456 is therefore 1.3 times more luminous than 3C 273 and the most luminous quasar in the nearby (z • 0.3) universe. Subject headings: infrared: general — quasars: individual (PDS 456, IRAS 17254 21413) — X-rays: galaxies

Statistical fractal analysis of 25 young star clusters

A large sample of young stellar groups is analysed aiming to investigate their clustering properties and dynamical evolution. A comparison of the Q statistical parameter, measured for the clusters, with the fractal dimension estimated for the projected clouds shows that 52% of the sample has substructures and tends to follow the theoretically expected relation between clusters and clouds, according to calculations for artificial distribution of points. The fractal statistics was also compared to structural parameters revealing that clusters having radial density profile show a trend of parameter s increasing with mean surface stellar density. The core radius of the sample, as a function of age, follows a distribution similar to that observed in stellar groups of Milky Way and other galaxies. They also have dynamical age, indicated by their crossing time, that is similar to unbound associations. The statistical analysis allowed us to separate the sample into two groups showing different clustering characteristics. However, they have the same dynamical evolution, since the whole sample has been revealed as expanding objects, for which the substructures seem to have not been erased. These results are in agreement with simulations that adopt low surface densities and models under supervirial conditions.

Characterisation of young stellar clusters

A high number of embedded clusters is found in the Galaxy. Depending on the formation scenario, most of them can evolve to unbounded groups that are dissolved within a few tens of Myr. A systematic study of young stellar clusters showing distinct characteristics provide interesting information on the evolutionary phases during the pre-main sequence. In order to identify and to understand these phases we performed a comparative study of 21 young stellar clusters. Near-infrared data from 2MASS were used to determine the structural and fundamental parameters based on surface stellar density maps, radial density profile, and colour-magnitude diagrams. We obtained age and mass distributions by comparing pre-main sequence models with the position of cluster members in the colour-magnitude diagram. The mean age of our sample is ~ 5 Myr, where 57% of the objects is found in the 4 - 10 Myr range of age, while 43% is < 4 Myr old. Their low E(B-V) indicate that the members are not suffering high extinction Av < 1 mag), which means they are more likely young stellar groups than embedded clusters. Relations between structural and fundamental parameters were used to verify differences and similarities that could be found among the clusters. The parameters of most of the objects have the same trends or correlations. Comparisons with other young clusters show similar relations among mass, radius and density. Our sample tends to have larger radius and lower volumetric density, when compared to embedded clusters. These differences are compatible with the mean age of our sample, which we consider intermediary between the embedded and the exposed phases of the stellar clusters evolution.

ANALYSIS OF THE PICO DOS DIAS SURVEY HERBIG Ae/Be CANDIDATES ∗

A large sample of Herbig Ae/Be (HAeBe) candidates, distributed in different Galactic regions south to declination +30°, were identified by the Pico dos Dias Survey (a search for young stellar objects based on IRAS colors). Most of the candidates are nearby or associated with star-forming clouds, but several others are considered isolated objects. Aiming to verify the young nature of 93 HAeBe candidates, we searched for additional information that could be useful to confirm if they are pre-main-sequence (PMS) stars or evolved objects, which coincidentally show similar IRAS colors. By adopting a spectral index that is related to the amount of infrared excess and the shape of the spectral energy distribution, we have classified the sample according to three groups, which are analyzed on the basis of (1) circumstellar luminosity; (2) spatial distribution; (3) optical polarization; (4) near-infrared colors; (5) stellar parameters (mass, age, effective temperature); and (5) intensity of emission lines. Our analysis indicates that only 76% of the studied sample, mainly the group with intermediate to low levels of circumstellar emission, can be more confidently considered PMS stars. The nature of the remaining stars, which are in the other group that contains the highest levels of infrared excess, remains to be confirmed. They share the same characteristics of evolved objects, requiring complementary studies in order to correctly classify them. At least seven objects show characteristics typical of post-asymptotic giant branch or proto-planetary nebulae.

The use of genetic algorithms to model protoplanetary discs

The protoplanetary discs of T Tauri and Herbig Ae/Be stars have previously been studied using geometric disc models to fit their spectral energy distribution (SED). The simulations provide a means to reproduce the signatures of various circumstellar structures, which are related to different levels of infrared excess. With the aim of improving our previous model, which assumed a simple flat-disc configuration, we adopt here a reprocessing flared-disc model that assumes hydrostatic, radiative equilibrium. We have developed a method to optimize the parameter estimation based on genetic algorithms (GAs). This paper describes the implementation of the new code, which has been applied to Herbig stars from the Pico dos Dias Survey catalogue, in order to illustrate the quality of the fitting for a variety of SED shapes. The star AB Aur was used as a test of the GA parameter estimation, and demonstrates that the new code reproduces successfully a canonical example of the flared-disc model. The GA method gives a good quality of fit, but the range of input parameters must be chosen with caution, as unrealistic disc parameters can be derived. It is confirmed that the flared-disc model fits the flattened SEDs typical of Herbig stars; however, embedded objects (increasing SED slope) and debris discs (steeply decreasing SED slope) are not well fitted with this configuration. Even considering the limitation of the derived parameters, the automatic process of SED fitting provides an interesting tool for the statistical analysis of the circumstellar luminosity of large samples of young stars.

Optical Polarization and Near-Infrared Photometry of the Proto-planetary Nebula Henize 3-1475*

We present BVRI CCD aperture polarization and near-infrared photometry of the proto-planetary nebula Hen 3-1475. Its intrinsic polarization is high and shows a strong spectral dependence. The position angles in all bands are perpendicular to the axis of the observed bipolar structure. A Monte Carlo code is used to model the intrinsic polarization of Hen 3-1475. Using disk dimensions and other constraints suggested by previous works, we are able to reproduce the observations with an optically thick disk composed by grains with a power-law size distribution ranging from 0.06 to 0.22 μm. We also reliably estimate the foreground polarization from hundreds of stars contained in the CCD images. It is parallel to the intrinsic polarization of Hen 3-1475. Possible implications of this result are discussed. From IR observations, we estimate an interstellar reddening, AV, of about 3.2.

Star formation history of Canis Major R1 - I. Wide-Field X-ray study of the young stellar population

Aims. The CMa R1 star-forming region contains several compact clusters as well as many young early-B stars. It is associated with a well-known bright rimmed nebula, the nature of which is unclear (fossil HII region or supernova remnant). To help elucidate the nature of the nebula, our goal was to reconstruct the star-formation history of the CMa R1 region, including the previously unknown older, fainter low-mass stellar population, using X-rays. Methods. We analyzed images obtained with the ROSAT satellite, covering ∼5 sq. deg. Complementary VRI photometry was performed with the Gemini South telescope. Colour-magnitude and colour-colour diagrams were used in conjunction with pre-main sequence evolutionary tracks to derive the masses and ages of the X-ray sources. Results. The ROSAT images show two distinct clusters. One is associated with the known optical clusters near Z CMa, to which ∼40 members are added. The other, which we name the “GU CMa” cluster, is new, and contains ∼60 members. The ROSAT sources are young stars with masses down to M� ∼ 0.5 M� , and ages up to 10 Myr. The mass functions of the two clusters are similar, but the GU CMa cluster is older than the cluster around Z CMa by at least a few Myr. Also, the GU CMa cluster is away from any molecular cloud, implying that star formation must have ceased; on the contrary (as already known), star formation is very active in the Z CMa region.

Probing the anomalous extinction of four young star clusters: the use of colour-excess, main-sequence fitting and fractal analysis

Aims. We studied four young star clusters to characterise their anomalous extinction or variable reddening and asses whether they could be due to contamination by either dense clouds or circumstellar effects. Methods. We evaluated the extinction law (RV) by adopting two methods: (i) the use of theoretical expressions based on the colourexcess of stars with known spectral type; and (ii) the analysis of two-colour diagrams, where the slope of the observed colour distribution was compared to the normal distribution. An algorithm to reproduce the zero-age main-sequence (ZAMS) reddened colours was developed to derive the average visual extinction (AV) that provides the closest fit to the observational data. The structure of the clouds was evaluated by means of a statistical fractal analysis, designed to compare their geometric structure with the spatial distribution of the cluster members. Results. The cluster NGC 6530 is the only object of our sample affected by anomalous extinction. On average, the other clusters suffer normal extinction, but several of their members, mainly in NGC 2264, seem to have high RV, probably because of circumstellar effects. The ZAMS fitting provides AV values that are in good agreement with those found in the literature. The fractal analysis shows that NGC 6530 has a centrally concentrated distribution of stars that differs from the substructures found in the density distribution of the cloud projected in the AV map, suggesting that the original cloud was changed by the cluster formation. However, the fractal dimension and statistical parameters of Berkeley 86, NGC 2244, and NGC 2264 indicate that there is a good cloud-cluster correlation, when compared to other works based on an artificial distribution of points.