12 research outputs found
Analysis of the stellar population in the central area of the HII region Sh 2-284
There is a lack of state-of-the-art information on very young open clusters,
with implications for determining the structure of the Galaxy. Our main
objective is to study the timing and location of the star formation processes
which yielded the generation of the giant HII region Sh 2-284. The analysis is
based on UBVRcIc CCD measurements and JHKs photometry in the central part of
the HII region, where the cluster Dolidze 25 is located.The determination of
cluster distance, reddening and age is carried out through comparison with
ZAMS, post-MS and PMS isochrones. Reference lines for metallicity Z=0.004 are
used, in agreement with spectroscopic metallicity determination published for
several cluster members. The results are: E(B-V)=0.78+-0.02, M=12.8+-0.2,
LogAge(yr)=6.51+-0.07. A PMS member sequence is proposed, coeval within the
errors with the post-MS cluster age (LogAge(yr)=6.7+-0.2). The mass function
for this PMS population in the mass range above 1.3-3.5 Msun is well fitted by
a Salpeter mass function.The presence of a different star generation in the
cluster with a distinctly older age, around 40 Myr, is suggested. The NIR
results indicate a large number of sources with H-Ks excess, practically
distinct from the optical PMS candidate members.
The distance determined for the cluster is distinctly lower than previously
published values. This result originates in the consistent use of low
metallicity models for ZAMS fitting, applying published metallicity values for
the cluster.Comment: gzipped tar file: 1 aa.cls, 1 tex file, 1 bbl file, 13 figures.
Accepted in Astronomy & Astrophysics (9.11.2009
X-ray pulsar XTE J1858+034: discovery of the cyclotron line and the revised optical identification
We present results of a detailed investigation of the poorly studied X-ray
pulsar XTE J1858+034 based on the data obtained with the NuSTAR observatory
during the outburst of the source in 2019. The spectral analysis resulted in
the discovery of a cyclotron absorption feature in the source spectrum at ~48
keV both in the pulse phase averaged and resolved spectra. Accurate X-ray
localization of the source using the NuSTAR and Chandra observatories allowed
us to accurately determine the position of the X-ray source and identify the
optical companion of the pulsar. The analysis of the counterpart properties
suggested that the system is likely a symbiotic binary hosting an X-ray pulsar
and a late type companion star of K-M classes rather than Be X-ray binary as
previously suggested.Comment: 12 pages, 12 figures, accepted by Ap
X-Ray Pulsar XTE J1858+034: Discovery of the Cyclotron Line and the Revised Optical Identification
We present the results of a detailed investigation of the poorly studied X-ray pulsar (XRP) XTE J1858+034 based on the data obtained with the NuSTAR observatory during the outburst of the source in 2019. The spectral analysis resulted in the discovery of a cyclotron absorption feature in the source spectrum at similar to ~48 keV in both the pulse phase-averaged and resolved spectra. Accurate X-ray localization of the source using the NuSTAR and Chandra observatories allowed us to accurately determine the position of the X-ray source and identify the optical companion of the pulsar. The analysis of the counterpart properties suggested that the system is likely a symbiotic binary hosting an XRP and a late-type companion star of the K-M classes rather than a Be X-ray binary as previously suggested
Spectral Type and Geometric Albedo of (98943) 2001 CC21, the Hayabusa2# Mission Target
We conducted optical polarimetry and near-infrared spectroscopy of JAXA's
Hayabusa2# mission target, (98943) 2001 CC21, in early 2023. Our new
observations indicated that this asteroid has a polarimetric inversion angle of
~21 deg, absorption bands around 0.9 and 1.9 um, and a geometric albedo of
0.285 +- 0.083. All these features are consistent with those of S-type but
inconsistent with L-type. Based on this evidence, we conclude that JAXA's
Hayabusa2# spacecraft will explore an S-type asteroid with albedo and size
(0.42-0.56 km when we assume the absolute magnitude of 18.6) similar to (25143)
Itokawa.Comment: 5 pages, 3 figures, Submitted to MNRAS Letter on 2023 April
Near-infrared Characterization of Four Massive Stars in Transition Phases
Massive stars typically undergo short-lived post-main-sequence evolutionary phases with strong mass loss and occasional mass eruptions. Many of such massive stars in transition phases have been identified based on their dusty envelopes. The ejected material often veils the stellar photospheres so that the central stars cannot be assigned proper spectral types and evolutionary stages. The infrared spectral range has proved to be ideal for the classification of evolved massive stars and for the characterization of their environments. To improve our knowledge on the central stars of four such dust-enshrouded objects, [GKF 2010] MN 83, [GKF 2010] MN 108, [GKF 2010] MN 109, and [GKF 2010] MN 112, we collect and present their first medium-resolution K-band spectra in the 2.3-2.47 μm region and discuss the location of the stars in the JHK color-color diagram. We find that the emission-line spectra of both MN 83 and MN 112 show characteristics typically seen in luminous blue variable (LBV) stars. In addition, we propose that the presence and strength of the newly reported Mg II lines might be used as a new complementary criterion to identify LBV candidates. The spectra of the other two objects imply that MN 108 is an O-type supergiant, whereas MN 109 could be an LBV candidate in its active phase. We derive lower limits for the reddening toward the stars and find that three of all dereddened fall into the region of confirmed LBVs.Fil: Cochetti, Yanina Roxana. 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 Nacional de la Plata. Facultad de Cs.astronómicas y Geofísicas. Departamento de Espectrocopia Estelar; ArgentinaFil: Kraus, Michaela. Astronomical Institute, Czech Academy Of Sciences; República ChecaFil: Arias, María Laura. 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 Nacional de la Plata. Facultad de Cs.astronómicas y Geofísicas. Departamento de Espectrocopia Estelar; ArgentinaFil: Cidale, Lydia Sonia. Universidad Nacional de la Plata. Facultad de Cs.astronómicas y Geofísicas. Departamento de Espectrocopia Estelar; 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: Eenmäe, Tõnis. University Of Tartu. Faculty Of Science And Technology. Tartu Observatory.; EstoniaFil: Liimets, Tiina. University Of Tartu. Faculty Of Science And Technology. Tartu Observatory.; Estonia. Astronomical Institute, Czech Academy Of Sciences; República ChecaFil: Torres, Andrea Fabiana. Universidad Nacional de la Plata. Facultad de Cs.astronómicas y Geofísicas. Departamento de Espectrocopia Estelar; 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: Djupvik, Anlaug A.. Nordic Optical Telescope; Españ
Discovery of a pulse-phase-transient cyclotron line in the X-ray pulsar Swift J1808.4-1754 and identification of an optical companion
In this work, the temporal and spectral properties of the poorly studied
X-ray pulsar Swift J1808.41754 were investigated in the 0.8-79 keV energy
range based on the data from the NuSTAR and Swift observatories collected
during the 2014 outburst. Strong pulsations with a period of s
were detected in the source light curve, with the pulsed fraction demonstrating
a nonmonotonic dependence on the energy with a local minimum around 17-22 keV.
Phase lags in one of the pulse profile components, reaching the maximal value
approximately at the same energy, were discovered. The pulse phase-averaged
spectrum of the source has a power-law shape with an exponential cutoff at high
energies, which is typical of X-ray pulsars. Pulse phase-resolved spectroscopy
revealed the presence of a pulse phase-transient cyclotron absorption line at
21 keV, allowing us to estimate the neutron star magnetic field of
G. This makes Swift J1808.41754 a member of very small
family of X-ray pulsars with a pulse-phase-transient cyclotron line in a narrow
phase range. The data from the Nordic Optical Telescope allowed us to study the
properties of the IR companion in the system and to conclude that most probably
it is a Be-type star located at a distance of 5-8 kpc.Comment: Accepted for publication in MNRAS. 9 pages, 10 figures, 3 table
(3200) Phaethon polarimetry in the negative branch : new evidence for the anhydrous nature of the DESTINY (+) target asteroid
We report on the first polarimetric study of (3200) Phaethon, the target of JAXA's DESTINY+ mission, in the negative branch to ensure its anhydrous nature and to derive an accurate geometric albedo. We conducted observations at low phase angles (Sun-target-observer angle, alpha= 8.8-32.4 degrees) from 2021 October to 2022 January and found that Phaethon has a minimum polarization degree P-min = -1.3 +/- 0.1 per cent, a polarimetric slope h = 0.22 +/- 0.02 per cent deg (1), and an inversion angle alpha(0) = 19.9 +/- 0.3 degrees. The derived geometric albedo is p(V) = 0.11 (in the range of 0.08-0.13). These polarimetric properties are consistent with anhydrous chondrites, contradict hydrous chondrites, and typical cometary nuclei.Peer reviewe