We present a comprehensive data description for K sub(s)-band measurements of Sgr A*. We characterize the statistical properties of the variability of Sgr A* in the near-infrared, which we find to be ...consistent with a single-state process forming a power-law distribution of the flux density. We discover a linear rms-flux relation for the flux density range up to 12 mJy on a timescale of 24 minutes. This and the power-law flux density distribution implies a phenomenological, formally nonlinear statistical variability model with which we can simulate the observed variability and extrapolate its behavior to higher flux levels and longer timescales. We present reasons why data with our cadence cannot be used to decide on the question whether the power spectral density of the underlying random process shows more structure at timescales between 25 minutes and 100 minutes compared to what is expected from a red-noise random process.
It is often assumed that the strong gravitational field of a super-massive black hole disrupts an adjacent molecular cloud preventing classical star formation in the deep potential well of the black ...hole. Yet, young stars have been observed across the entire nuclear star cluster of the Milky Way including the region close (<0.5 pc) to the central black hole, Sgr A*. Here, we focus particularly on small groups of young stars, such as IRS 13N located 0.1 pc away from Sgr A*, which is suggested to contain about five embedded massive young stellar objects (<1 Myr). We perform three-dimensional hydrodynamical simulations to follow the evolution of molecular clumps orbiting about a 4 × 106 M⊙ black hole, to constrain the formation and the physical conditions of such groups. The molecular clumps in our models are assumed to be isothermal containing 100 M⊙ in <0.2 pc radius. Such molecular clumps exist in the circumnuclear disc of the Galaxy. In our highly eccentrically orbiting clump, the strong orbital compression of the clump along the orbital radius vector and perpendicular to the orbital plane causes the gas densities to increase to values higher than the tidal density of Sgr A*, which are required for star formation. Additionally, we speculate that the infrared excess source G2/DSO approaching Sgr A* on a highly eccentric orbit could be associated with a dust-enshrouded star that may have been formed recently through the mechanism supported by our models.
A spectrofluorimetric method for determining diclofenac sodium and propranolol hydrochloride in an aqueous medium has been described. The method is based on increasing the intensity of fluorescein ...dye fluorescence when diclofenac is added at an excitation wavelength of 353 nm and an emission wavelength of 513 nm, and quenching fluorescein dye fluorescence when propranolol is added at an excitation wavelength of 353 nm and an emission wavelength of 518 nm. The determination ranges for diclofenac sodium and propranolol hydrochloride were 2–18 and 0.2–7 µg/mL, respectively, with a limit of detection of 0.114 and 0.050 µg/mL, and a limit of quantitation of 0.382 and 0.170 µg/mL, respectively. The average recoveries were 100.25 and 97.95% with a relative standard deviation of less than 0.6% for both pharmaceuticals, respectively. The proposed method has been applied for the analysis of commercial tablets and injections containing the medications. A statistical comparison of the data with the official method revealed good agreement and demonstrated that there were no significant differences in the accuracy and precision of the two approaches.
Calcon dye has been used for spectrophotometric determination of catecholamine-containing drugs, namely, adrenaline, methyldopa and dopamine in their pure forms and pharmaceutical formulations. The ...method is based on the oxidation of the above drugs with an excess of Nbromosuccinimide (NBS) in an acidic medium. The residual oxidizing agent bleaches the blackish-brown color of calcon measured at 510 nm. The decolorization of the dye is proportional to the residual amount of NBS, which is proportional to the concentration of the drug. Linear calibration graphs were obtained in the concentration range 0.5-16.0, 2.0-40.0 and 1.036.0 μgmL -1 with molar absorptivity values 1.10×104 , 3.2×103 and 4.3×103 Lmol-1 cm-1 for above drugs, respectively. The method is simple, sensitive, accurate, precise and free from excipients. The developed method was successfully applied to determine the drugs in their pharmaceutical formulations.
Context. There are a number of faint compact infrared excess sources in the central stellar cluster of the Milky Way. Their nature and origin is unclear. In addition to several isolated objects of ...this kind there is a small but dense cluster of comoving sources (IRS13N) located ~3′′ west of SgrA* just 0.5′′ north of the bright IRS13E cluster of Wolf-Rayet and O-type stars. Based on the analysis of their color and brightness, there are two main possibilities: (1) they may be dust-embedded stars older than a few Myr; or (2) very young, dusty stars with ages younger than 1 Myr. Aims. We present a first Ks-band identification and proper motions of the IRS13N members, the high-velocity dusty S-cluster object (DSO, also referred to as G2), and other infrared excess sources in the central field. Goal is to constrain the nature of these source. Methods. The L′- (3.8 μm) Ks- (2.2 μm) and H-band (1.65 μm) observations were carried out using the NACO adaptive optics system at the ESO VLT. Proper motions were obtained by linear fitting of the stellar positions extracted by StarFinder as a function of time, weighted by positional uncertainties, and by Gaussian fitting from high-pass filtered and deconvolved images. We also present results of near-infrared (NIR) H- and Ks-band ESO-SINFONI integral field spectroscopy of the Galactic center cluster ISR13N. Results. We show that within the uncertainties, the positions and proper motions of the IRS13N sources in Ks- and L′-band are identical. The HK−sL′ colors then indicate that the bright L′-band IRS13N sources are indeed dust-enshrouded stars rather than core-less dust clouds. The proper motions also show that the IRS13N sources are not strongly gravitationally bound to each other. Combined with their NIR colors, this implies that they have been formed recently. For the DSO we obtain proper motions and a Ks-L′-color. Conclusions. Most of the compact L′-band excess emission sources have a compact H- or Ks-band counterpart and therefore are likely stars with dust shells or disks. Our new results and orbital analysis from our previous work favor the hypothesis that the infrared excess IRS13N members and other dusty sources close to SgrA* are young dusty stars and that star formation at the Galactic center (GC) is a continuously ongoing process. For the DSO the color information indicates that it may be a dust cloud or a dust-embedded star.
We investigate an infrared-excess source called G2 or Dusty S-cluster Object (DSO), which moves on a highly eccentric orbit around the Galaxy’s central black hole, Sgr A*. We use, for the first time, ...near-infrared polarimetric imaging data to determine the nature and properties of the DSO and obtain an improved Ks-band identification of this source in median polarimetry images of different observing years. The source started to deviate from the stellar confusion in 2008, and it does not show any flux density variability over the years we analyzed it. We measured the polarization degree and angle of the DSO between 2008 and 2012 and conclude, based on the significance analysis on polarization parameters, that it is an intrinsically polarized source (> 20%) with a varying polarization angle as it approaches the position of Sgr A*. The DSO shows a near-infrared excess of Ks−L′ > 3 that remains compact close to the pericenter of its orbit. Its observed parameters and the significant polarization obtained in this work show that the DSO might be a dust-enshrouded young star, forming a bow shock as it approaches the super massive black hole. The significantly high measured polarization degree indicates that it has a non-spherical geometry, and it can be modeled as a combination of a bow shock with a bipolar wind of the star. We used a 3D radiative transfer model that can reproduce the observed properties of the source such as the total flux density and the polarization degree. We obtain that the change of the polarization angle can be due to an intrinsic change in the source structure. Accretion disk precession of the young star in the gravitational field of the black hole can lead to the change of the bipolar outflow and therefore the polarization angle variation. It might also be the result of the source interaction with the ambient medium.
Context. We report on new simultaneous observations and modeling of the millimeter, near-infrared, and X-ray flare emission of the source Sagittarius A* (SgrA*) associated with the super-massive ...(4 × 106 M⊙) black hole at the Galactic center. Aims. We study the applicability of the adiabatic synchrotron source expansion model and study physical processes giving rise to the variable emission of SgrA* from the radio to the X-ray domain. Methods. Our observations were carried out on 18 May 2009 using the NACO adaptive optics (AO) instrument at the European Southern Observatory’s Very Large Telescope, the ACIS-I instrument aboard the Chandra X-ray Observatory, the LABOCA bolometer at the Atacama Pathfinder EXperiment (APEX), and the CARMA mm telescope array at Cedar Flat, California. Results. The X-ray flare had an excess 2 − 8 keV luminosity between 6 and 12 × 1033 erg s-1. The observations reveal flaring activity in all wavelength bands that can be modeled as the signal from an adiabatically expanding synchrotron self-Compton (SSC) component. Modeling of the light curves shows that the sub-mm follows the NIR emission with a delay of about three-quarters of an hour with an expansion velocity of about vexp ~ 0.009c. We find source component sizes of around one Schwarzschild radius, flux densities of a few Janskys, and spectral indices α of about +1 (S(ν) ∝ ν−α). At the start of the flare, the spectra of the two main components peak just short of 1 THz. To statistically explain the observed variability of the (sub-)mm spectrum of SgrA*, we use a sample of simultaneous NIR/X-ray flare peaks and model the flares using a synchrotron and SSC mechanism. Conclusions. These parameters suggest that either the adiabatically expanding source components have a bulk motion larger than vexp or the expanding material contributes to a corona or disk, confined to the immediate surroundings of SgrA*. For the bulk of the synchrotron and SSC models, we find synchrotron turnover frequencies in the range of 300−400 GHz. For the pure synchrotron models, this results in densities of relativistic particles of the order of 106.5 cm-3 and for the SSC models, the median densities are about one order of magnitude higher. However, to obtain a realistic description of the frequency-dependent variability amplitude of SgrA*, models with higher turnover frequencies and even higher densities are required.
For the past few years, we have observed the central half parsec of our Galaxy in the mid-infrared from 2.8 to 5.1 μm. Our aim is to improve our understanding of the direct environment of SgrA⋆, the ...super-massive black hole at the centre of the Milky Way. This work is described in the present paper and by Moultaka et al. Here, we focus on the study of the spatial distribution of the 12CO ice and gas-phase absorptions. We observed the central half parsec with ISAAC spectrograph located at the ut3/VLT ESO telescope in Chile. The slit was placed along 22 positions arranged parallel to each other to map the region. We built the first data cube in this wavelength range covering the central half parsec. The wavelength interval of the used M-band filter ranges from 4.6 to 5.1 μm. It hosts the P- and R- branches of the ro-vibrational transitions of the gaseous 12CO and 13CO, as well as the absorption band attributed to the 12CO ice at 4.675 μm. Using two calibrators, we could disentangle the local from the line-of-sight absorptions and provide a first-order estimate of the foreground extinction. We find residual ices and gas-phase CO that can be attributed to local absorptions due to material from the interstellar and/or the circumstellar medium of the central parsec. Our finding implies temperatures of the order of 10 to 60 K which is in agreement with the presence of water ices in the region highlighted by Moultaka et al
A sensitive spectrofluorimetric method has been developed for the analysis of some medicines containing primary, secondary, and tertiary amino groups, namely Diclofenac (DIC), Domperidone (DOM), ...Famotidine (FAM), and Propranolol (PRO), in their pure and medicinal forms. The method is based on the quenching of the fluorescence intensity of rhodamine 6G (R6G) through the formation of ion-pair complexes between the above medicines and the R-6G reagent, which is measured at 552 nm after excitation at 402 nm. The calibration graphs were rectilinear in the concentration ranges of 0.10- 9.00, 0.05-15.00, 0.10-14.0 and 0.05-5.00 µg mL-1 for above medicines respectively. The recovery (%) values were ranged between 99.45%- 100.97%. The detection limits ranged in the concentration of 0.243-0.754 µg/mL, and the limits of quantitation were 0.806- 2.420 µgmL-1 for all drugs. The method was successfully applied for the determination of these drugs in their pharmaceutical preparations.
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