In this paper, we report the results of spectroscopic and photometric observations of the candidate evolved massive star MN48 disclosed via detection of a mid-infrared circular shell around it with ...the Spitzer Space Telescope. Follow-up optical spectroscopy of MN48 with the Southern African Large Telescope (SALT) carried out in 2011-2015 revealed significant changes in the spectrum of this star, which are typical of luminous blue variables (LBVs). The LBV status of MN48 was further supported by photometric monitoring which shows that in 2009-2011 this star has brightened by ...0.9 and 1 mag in the V and I sub( c) bands, respectively, then faded by ...1.1 and 1.6 mag during the next four years, and apparently started to brighten again recently. The detected changes in the spectrum and brightness of MN48 make this star the 18th known Galactic bona fide LBV and increase the percentage of LBVs associated with circumstellar nebulae to more than 70 per cent. We discuss the possible birth place of MN48 and suggest that this star might have been ejected either from a putative star cluster embedded in the H ii region IRAS 16455-4531 or the young massive star cluster Westerlund 1. (ProQuest: ... denotes formulae/symbols omitted.)
We use US Naval Observatory CCD Astrograph Catalogue (UCAC4) proper motions and Wide-Field Infrared Survey Explorer (WISE) W1-band apparent magnitudes and intensity means for almost 400 field RR ...Lyrae variables to determine the parameters of the velocity distribution of the Galactic RR Lyrae population and constrain the zero-points of the metallicity-〈M
V
〉, period-metallicity-〈 MKs
〉-band and period-metallicity-〈M
W1〉-band luminosity relations via statistical parallax. We find the mean velocities of the halo- and thick-disc RR Lyrae populations in the solar neighbourhood to be U
0(Halo), V
0(Halo), W
0(Halo) = (−7 ± 9, −214 ± 10, −10 ± 6) km s−1 and U
0(Disc), V
0(Disc), W
0(Disc) = (−13 ± 7, −37 ± 6, −17 ± 4) km s−1, respectively, while the corresponding components of the velocity-dispersion ellipsoids are σV
R
(Halo), σV
φ(Halo), σV
θ(Halo) = (153 ± 9, 101 ± 6, 96 ± 5) km s−1 and σV
R
(Disc), σV
φ(Disc), σV
θ(Disc) = (46 ± 7, 37 ± 5, 27 ± 4) km s−1, respectively. The fraction of thick-disc stars is estimated at 0.22 ± 0.03. The corrected infrared period-metallicity-luminosity relations are
and
and the optical metallicity-luminosity relation Fe/H-〈M
V
〉 is 〈M
V
〉 = +1.094 + 0.232Fe/H with a standard error of ±0.089, implying a Large Magellanic Cloud distance modulus of 18.32 ± 0.09, a solar Galactocentric distance of 7.73 ± 0.36 kpc and M31 and M33 distance moduli of DM
M31 = 24.24 ± 0.09 (D = 705 ± 30 kpc) and DM
M33 = 24.36 ± 0.09 (D = 745 ± 31 kpc), respectively. Extragalactic distances calibrated with our RR Lyrae star luminosity scale imply a Hubble constant of ∼80 km s−1 Mpc−1. Our results suggest marginal prograde rotation for the population of halo RR Lyraes in the Milky Way.
The paper presents recent PHENIX results on hadron production in heavy ion collisions. Comparison of light hadron (
,
,
,
,
,
,
,
,
) nuclear modification factors in Au
Au, Cu
Au collisions at
GeV ...and U
U collisions at
GeV will be discussed.
ABSTRACT
This paper presents results from photometric and statistical-parallax analysis of a sample of 850 field RR Lyrae (RRL) variables. The photometric and spectroscopic data for our sample of ...RRLs are obtained from (1) our new spectroscopic observations (for 448 RRLs) carried out with the Southern African Large Telescope; (2) our photometric observations using the 1.0-m telescope of the South African Astronomical Observatory, and (3) literature. These are combined with accurate proper motion data from the second data release of the Gaia mission (DR2). This study primarily determines the velocity distribution of solar neighbourhood RRLs, and it also calibrates the zero-points of the RRLs’ visual V-band luminosity–metallicity (LZ or MV–Fe/H) relation and their period–luminosity–metallicity (PLZ) relations in the Wide-field Infrared Survey ExplorerW1 and Two-Micron All-Sky Survey Ks bands. We find the bulk velocity of the halo RRLs relative to the Sun to be (U0, V0, W0)Halo =(− 16 ± 7, −219 ± 7, −6 ± 5) km s−1 in the direction of Galactic centre, Galactic rotation, and North Galactic pole, respectively, with velocity-dispersion ellipsoids (σVR, σVϕ, σVθ)Halo = (153 ± 7, 106 ± 4, 101 ± 4) km s−1. The corresponding parameters for the disc component are found to be (U0, V0, W0)Disc = (− 19 ± 5, −46 ± 5, −14 ± 3) km s−1 and (σVR, σVϕ, σVθ)Disc =(49 ± 4, 38 ± 4, 25 ± 3) km s−1. The calibrated PLZ in W1-, Ks-, and V-band LZ relations are $\langle \, M_{W1}\rangle =$ $-0.824+0.124\mathrm{ Fe/H}-2.381\log \, P_F$, 〈MKs〉 = $-0.804+0.101\mathrm{ Fe/H}-2.33\log \, P_F$, and $\langle \, M_V\rangle =1.041+0.232\mathrm{ Fe/H}$, respectively. The calibrated PLZ and LZ relations are used to estimate the Galactic Centre distance and the distance modulus of the Large Magellanic Cloud (LMC), which are found to be 7.99 ± 0.49 kpc and 18.46 ± 0.09 mag, respectively. All our results are in excellent agreement with available literature based on statistical-parallax analysis, but are considerably more accurate and precise. Moreover, the zero-points of our calibrated PLZ and LZ relations are quite consistent with current results found by other techniques and yield an LMC distance modulus that is within 0.04 mag of the current most precise estimate.
The paper presents the results on
,
and
production in small collision systems at
GeV as a function of transverse momentum at midrapidity (
) measured by the PHENIX experiment.
We report the results of optical spectroscopy of the candidate evolved massive star MN44 revealed via detection of a circular shell with the Spitzer Space Telescope. First spectra taken in 2009 ...May–June showed the Balmer lines in emission as well as numerous emission lines of iron, which is typical of luminous blue variables (LBVs) near the visual maximum. New observations carried out in 2015 May–September detected significant changes in the spectrum, indicating that the star became hotter. We found that these changes are accompanied by significant brightness variability of MN44. In particular, the I
c-band brightness decreased by ≈ 1.6 mag during the last six years and after reaching its minimum in 2015 June has started to increase. Using archival data, we also found that the I
c-band brightness increased by ≈3 mag in ≈30 yr preceding our observations. MN44 therefore represents the 17th known example of the Galactic bona fide LBVs. We detected a nitrogen-rich knot to the north-west of the star, which might represent an interstellar cloudlet interacting with the circumstellar shell. We discuss a possible association between MN44 and the INTEGRAL transient source of hard X-ray emission IGR J16327−4940, implying that MN44 might be either a colliding-wind binary or a high-mass X-ray binary.
We report the results of spectrophotometric observations of the massive star MN18 revealed via discovery of a bipolar nebula around it with the Spitzer Space Telescope. Using the optical spectrum ...obtained with the Southern African Large Telescope, we classify this star as B1 Ia. The evolved status of MN18 is supported by the detection of nitrogen overabundance in the nebula, which implies that it is composed of processed material ejected by the star. We analysed the spectrum of MN18 by using the code cmfgen, obtaining a stellar effective temperature of ≈21 kK. The star is highly reddened, E(B − V) ≈ 2 mag. Adopting an absolute visual magnitude of M
V = −6.8 ± 0.5 (typical of B1 supergiants), MN18 has a luminosity of log L/L⊙ ≈ 5.42 ± 0.30, a mass-loss rate of ≈(2.8-4.5) × 10− 7 M⊙ yr− 1, and resides at a distance of ≈5.6
$^{+1.5} _{-1.2}$
kpc. We discuss the origin of the nebula around MN18 and compare it with similar nebulae produced by other blue supergiants in the Galaxy
(Sher 25, HD 168625, SBW2007 1) and the Large Magellanic Cloud (Sk−69
$\deg$
202). The nitrogen abundances in these nebulae imply that blue supergiants can produce them from the main-sequence stage up to the pre-supernova stage. We also present a K-band spectrum of the candidate luminous blue variable MN56 (encircled by a ring-like nebula) and report the discovery of an OB star at ≈17 arcsec from MN18. The possible membership of MN18 and the OB star of the star cluster Lynga 3 is discussed.
Abstract
We report the results of optical spectroscopy of the blue supergiant Sk−69° 279 and its circular shell in the Large Magellanic Cloud (LMC) with the Southern African Large Telescope (SALT). ...We classify Sk−69° 279 as an O9.2 Iaf star and analyse its spectrum by using the stellar atmosphere code cmfgen, obtaining a stellar temperature of ≈30 kK, a luminosity of log (L*/ L⊙) = 5.54, a mass-loss rate of $\log (\dot{M}/\rm \, M_{\odot }\, {\rm yr}^{-1}$) = −5.26, and a wind velocity of 800km s−1. We found also that Sk−69° 279 possesses an extended atmosphere with an effective temperature of ≈24 kK and that its surface helium and nitrogen abundances are enhanced, respectively, by factors of ≈2 and 20–30. This suggests that either Sk−69° 279 was initially a (single) fast-rotating ( ≳ 400 km s− 1) star, which only recently evolved off the main sequence, or that it is a product of close binary evolution. The long-slit spectroscopy of the shell around Sk−69° 279 revealed that its nitrogen abundance is enhanced by the same factor as the stellar atmosphere, which implies that the shell is composed mostly of the CNO processed material lost by the star. Our findings support previous propositions that some massive stars can produce compact circumstellar shells and, presumably, appear as luminous blue variables while they are still on the main sequence or have only recently left it.
ABSTRACT
We present the results of study of the Galactic candidate luminous blue variable Wray 15-906, revealed via detection of its infrared circumstellar shell (of ≈2 pc in diameter) with the ...Wide-field Infrared Survey Explorer and the Herschel Space Observatory. Using the stellar atmosphere code cmfgen and the Gaia parallax, we found that Wray 15-906 is a relatively low-luminosity, $\log (L/\rm \, L_\odot)\approx 5.4$, star of temperature of 25 ± 2 kK, with a mass-loss rate of ${\approx}3\times 10^{-5} \, \rm \, M_\odot \, {\rm yr}^{-1}$, a wind velocity of $280\pm 50 \, {\rm \, km\, s^{-1}}$, and a surface helium abundance of 65 ± 2 per cent (by mass). In the framework of single-star evolution, the obtained results suggest that Wray 15-906 is a post-red supergiant star with initial mass of ${\approx}25 \, \rm \, M_\odot$ and that before exploding as a supernova it could transform for a short time into a WN11h star. Our spectroscopic monitoring with the Southern African Large Telescope does not reveal significant changes in the spectrum of Wray 15-906 during the last 8 yr, while the V-band light curve of this star over years 1999–2019 shows quasi-periodic variability with a period of ≈1700 d and an amplitude of ≈0.2 mag. We estimated the mass of the shell to be $2.9\pm 0.5 \, \rm \, M_\odot$ assuming the gas-to-dust mass ratio of 200. The presence of such a shell indicates that Wray 15-906 has suffered substantial mass-loss in the recent past. We found that the open star cluster C1128−631 could be the birth place of Wray 15-906 provided that this star is a rejuvenated product of binary evolution (a blue straggler).
Nuclear modification factor
R
AA
of π
0
mesons produced in
3
HeAu collisions at a cms energy of
= 200 GeV is extracted from data of the PHENIX experiment at the RHIC. The mean
R
AA
value for π
0
... mesons with
p
T
> 8 GeV/
c
is found to be close to 0.8 for central
3
He + Au collisions.
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