1,721,313 research outputs found
A Survey of N IV and O IV Features near 3400 Å in O2-O5 Spectra
Full text linkWe have conducted a survey of little-known N iv and O iv multiplets near 3400 A˚ in an extensive sample of well-classified, very early O-type spectra. The initial motivation was to search for additional useful classification criteria for these types, but an unexpected result is the high sensitivity of these features to evolutionary CNO processing. We have found a useful discriminant between O2 and later types in the relative strengths of the O iv multiplets, one of which is subject to selective emission in the hottest spectra; the overall strengths of these lines also decrease between spectral types O4 and O5. More remarkable, however, are the variations in the N/O ratios among both individual stars and clusters. For instance, several O4 If spectra have very large ratios, while main-sequence stars in the Carina Nebula generally have smaller values than others of the same spectral types in other regions. These effects correspond to different degrees of mixing of processed material as a function of evolutionary age and initial rotational velocities; the second effect provides significant further evidence that very massive stars mix while still on the main sequence. Thus, further analysis of these features will likely provide valuable diagnostics of important evolutionary parameters.Fil: Morrell, Nidia Irene. Las Campanas Observatory; ChileFil: Walborn, Nolan Revere. Space Telescope Science Institute; Estados UnidosFil: Arias, Julia Ines. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentin
Pre-main-sequence stars in the Lagoon Nebula (M8)
Full text linkWe report the discovery of new pre-main-sequence (PMS) stars in the Lagoon Nebula (M8) at a distance of 1.25 kpc, based on intermediate-resolution spectra obtained with the Boiler & Chivens spectrograph at the 6.5-m Magellan I Telescope (Las Campanas Observatory, Chile). According to the spectral types, the presence of emission lines and the lithium λ 6708 absorption line, we are able to identify 27 classical T Tauri stars, seven weak-lined T Tauri stars and three PMS emission objects with spectral type G, which we include in a separate stellar class denominated 'PMS Fe/Ge class'. Using near-infrared photometry either from the Two-Micron All-Sky Survey or from our own previous work, we derive effective temperatures and luminosities for these stars and locate them in the Hertzsprung-Russell diagram, in order to estimate their masses and ages. We find that almost all of our sample stars are younger than 3 × 106 yr and span over a range of masses between 0.8 and 2.5 M⊙. A cross-correlation between our spectroscopic data and the X-ray sources detected with the Chandra ACIS instrument is also presented.Fil: Arias, Julia Ines. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Barba, Rodolfo Hector. Universidad de La Serena; Chile. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Morrell, Nidia Irene. Las Campanas Observatory; Chile. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin
Havlen-Moffat #1, el cúmulo menos pensado
Full text linkThe cluster Havlen-Moffat # 1 (HM1), in the constellation of Scorpius, owes its name to those who discovered it in 1977. They identified, spectroscopically, two Wolf-Rayet and two Of-type stars. HM1 is located in the fourth quadrant of the Milky Way where the absorption of the interstellar medium is significant. This work presents an analysis of the fundamental parameters of the cluster, calculated by spectroscopy and UBVRI" role="presentation">UBVRI photometry of some of the brightest components whose data were obtained with the Swope and du Pont telescopes of Las Campanas, Chile. New OB-type stars were identified from these data and the possible presence of a supergiant M star was analyzed.El cúmulo Havlen-Moffat #1 (HM1), en la constelación de Escorpio, debe su nombre a quienes lo descubrieron en el año 1977. Ellos identificaron dos estrellas tipo Wolf-Rayet y dos estrellas tipo Of. HM1 se encuentra en el cuarto cuadrante de la Vía Láctea donde la absorción del medio interestelar es significativa. En este trabajo se presenta un análisis de los parámetros fundamentales del cúmulo calculados mediante espectroscopía y fotometría UBV RI de algunas de las componentes más brillantes, cuyos datos se obtuvieron con los telescopios Swope y du Pont de Las Campanas, Chile. A partir de estos datos se identificaron nuevas estrellas tipo OB y se analizó la posible presencia de una estrella supergigante M.Fil: Leiva, M. M.. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Giorgi, E. E.. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Gamen, Roberto Claudio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Morrell, Nidia Irene. Carnegie Institution; Chile. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina61° Reunión Anual de la Asociación Argentina de AstronomíaViedmaArgentinaUniversidad Nacional de Río NegroInstituto Argentino de Radioastronomí
Exploring massive star early evolution: the case of the Herschel 36 A triple system
No full textTheoretical models show that some massive stars have not yet arrived at the zero-age main sequence (ZAMS) at the end of the accretion phase. At that time, they have lost their thick envelopes and thus could be optically visible. Although some candidates to optically observable ZAMS stars have been reported, the evolutionary status of none of them has been confirmed yet. The O-type triple system Herschel 36 A (H36A) is one of these candidates. We present the quantitative spectral analysis of the individual stellar components of H36A and investigate the evolutionary status of the system by contrasting main-sequence and pre-main-sequence models. Overall, the derived parameters suggest that the components of H36A could be pre-main-sequence stars going through the very last contraction to the ZAMS. However, the possibility of them already being on the main sequence is not yet ruled out. This study highlights the importance of considering multiple evolutionary models and shows that H36A represents a key object for understanding massive star formation and early evolution.Fil: Arias, Julia Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; Argentina. Universidad de La Serena; ChileFil: Holgado, Gonzalo. Instituto de Astrofísica de Canarias; EspañaFil: Gamen, Roberto Claudio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Morrell, Nidia Irene. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; Argentina. Observatorio Las Campanas; ChileFil: Campillay, Abdo R.. Universidad de La Serena; Chil
A ~ 40 year variability cycle in the luminous blue variable/Wolf-Rayet Binary System HD 5980?
Full text linkThe massive Wolf-Rayet stellar system HD 5980 in the Small Magellanic Cloud entered a sudden and brief ~ 1-3 mag eruptive state in the mid-1990s. The cause of the instability is not yet understood, but mechanisms similar to those in luminous blue variables are suspected. Using a previously unreported set of spectroscopic data obtained in 1955-1967 and recently acquired optical and HST/STIS spectra, we find that (1) the brief eruptions of 1993 and 1994 occurred at the beginning of an extended (~ decades) high state of activity characterized by large emission-line intensities; (2) the level of activity is currently subsiding; and (3) another strong emission-line episode appears to have occurred between 1960 and 1965, suggesting the possibility that the long-term cyclical variability may be recurrent on a ~ 40 year timescale. These characteristics suggest the possible classification of HD 5980 as an S Doradus-type variable. The effects due to binary interactions in the system are discussed, and we tentatively suggest that the short duration and relatively hot spectral type (WN11/B1.5I) observed during maximum in the visual light curve may be attributed to these interactions.Fil: Koenigsberger, Gloria. Universidad Nacional Autónoma de México; MéxicoFil: Georgiev, Leonid. Universidad Nacional Autónoma de México; MéxicoFil: Hillier, D. John. University Of Pittsburgh; Estados UnidosFil: Morrell, Nidia Irene. The Carnegie Observatories. Las Campanas Observatory; Chile. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Barba, Rodolfo Hector. Consejo Nacional de Investigaciones Cientiâficas y Tecnicas. Centro Cientifico Tecnologico San Juan. Instituto de Ciencias Astronomicas de la Tierra y del Espacio; Argentina. Universidad de la Serena; ChileFil: Gamen, Roberto Claudio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Astrofísica de la Plata; Argentin
Giant HII regions in NGC7479 and NGC6070
Full text linkWe present new results from our search for Giant H ii Regions in galaxies visible
from the southern hemisphere. In this work we study two galaxies: NGC 7479 and
NGC 6070. Using high-resolution spectra, obtained with different instruments at Las
Campanas Observatory, we are able to resolve the emission-line profile widths and determine
the intrinsic velocity dispersion of the ionised gas. We detect profile widths corresponding
to supersonic velocity dispersions in the six observed H ii regions. We find
that all of them show at least two distinct kinematical components: a relatively narrow
feature (between 11 and 22 km s−1
) and a broader (between 31 and 77 km s−1
)
component. Two of the regions show a complex narrow profile in all ion lines, which
can be further split into two components with different radial velocities. Whereas the
wing broadening of the overall profile can be fitted with a low intensity broad component
for almost all profiles, in one region it was better reproduced by two separate
shell-like wings. We have analysed the impact that the presence of multiple
components has on the location of the Hii regions in the log(L) − log(σ)
plane. Although the overall distribution confirms the presence of a regression,
the precise location of the regions in the plane is strongly dependent
on the components derived from the profile fitting.Fil: Firpo, Verónica. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Bosch, Guillermo Luis. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Hägele, G. F.. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Universidad Autónoma de Madrid; EspañaFil: Morrell, Nidia Irene. Carnegie Observatories. Las Campanas Observatory; Chil
A double-lined spectroscopic binary in the open cluster Trumpler 14
Full text linkWe present the results of a determination of the preliminary orbital elements of the spectroscopic binary FMM 3 in the field of the open cluster Trumpler 14. The spectrum of this binary shows two sets of lines that are roughly similar. The period found was around 5 days (P = 5.0339 ± 0.0003), and the orbit is eccentric (e = 0.51 ± 0.02). These values were adopted from the combined solution for both components. The mass ratio of the system is 0.76 ± 0.06.Fil: Levato, Orlando Hugo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; ArgentinaFil: Malaroda, Stella Maris. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; ArgentinaFil: Morrell, Nidia Irene. Universidad Nacional de La Plata; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: García, Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Regional de Investigaciones Cientifícas y Tecnológicas; ArgentinaFil: Grosso, Monica Gladys. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; Argentin
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
SERENDIPITOUS DISCOVERY OF AN INFRARED BOW SHOCK NEAR PSR J1549-4848 WITH SPITZER
No full textWe report on the discovery of an infrared cometary nebula around PSR J1549-4848 in our Spitzer survey of a few middle-aged radio pulsars. Following the discovery, multi-wavelength imaging and spectroscopic observations of the nebula were carried out. We detected the nebula in Spitzer Infrared Array Camera 8.0, Multiband Imaging Photometer for Spitzer 24 and 70 mu m imaging, and in Spitzer IRS 7.5-14.4 mu m spectroscopic observations, and also in the Wide-field Infrared Survey Explorer all-sky survey at 12 and 22 mu m. These data were analyzed in detail, and we find that the nebula can be described with a standard bow shock shape, and that its spectrum contains polycyclic aromatic hydrocarbon and H-2 emission features. However, it is not certain which object drives the nebula. We analyze the field stars and conclude that none of them can be the associated object because stars with a strong wind or mass ejection that usually produce bow shocks are much brighter than the field stars. The pulsar is approximately 15 '' away from the region in which the associated object is expected to be located. In order to resolve the discrepancy, we suggest that a highly collimated wind could be emitted from the pulsar and produce the bow shock. X-ray imaging to detect the interaction of the wind with the ambient medium-and high-spatial resolution radio imaging to determine the proper motion of the pulsar should be carried out, which will help verify the association of the pulsar with the bow shock nebula
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